The government of Turkey, a NATO
member with the alliance's second largest army, had had a relatively friendly relationship with Syria over a decade prior to the start of the civil unrest in Syria in 2011; Turkey, while joining calls for the Syrian government to end the violence,
initially objected to the demand voiced in August 2011 by the US that Bashar Assad resign.
Turkey trained defectors from the Syrian Army on its territory, and in July 2011 a group of them announced the birth of the Free Syrian Army
In October 2011, Turkey began sheltering the Free Syrian Army, offering the group a safe zone and a base of operation. Together with Saudi Arabia
, Turkey has also provided the rebels with arms and other military equipment. Tensions between Syria and Turkey significantly worsened after Syrian forces shot down
a Turkish fighter jet in June 2012 and border clashes
in October 2012.
In early February 2016, Reuters referred to Turkey as "a major sponsor of the insurgency against President Bashar al-Assad".
Turkey provided refuge for Syrian dissidents from early days of the Syrian conflict. In early June 2011, Syrian opposition activists convened in Istanbul to discuss regime change,
and Turkey hosted the head of the Free Syrian Army, Colonel Riad al-Asaad.
Turkey became increasingly hostile to the Assad government's policies and came to encourage reconciliation among dissident factions. Recep Tayyip Erdoğan
has tried to "cultivate a favorable relationship with whatever government would take the place of Assad."
In May 2012, Syrian opposition forces started to receive arms and training from Turkey and the United States.
Turkey's subsequent arrangements with Russia and Iran (from early 2017) caused a rift in its relationship with the Syrian opposition, as the opposition leaders criticized Russia's plan to create safe zones in Syria as threatening the country's territorial integrity.
Turkey maintained a small enclave within Syria itself, the Tomb of Suleyman Shah
on the right bank of the Euphrates in Aleppo Province near the village of Qarah Qawzak (Karakozak). The tomb is guarded by a small permanent garrison of Turkish soldiers, who rotate in from a battalion based at the Turkish border some 25 kilometres (16 mi) away—even as the civil war unfolded around them.
Up until Syrian forces shot down a Turkish warplane
in June 2012, the garrison numbered 15 men in total. Following the incident, the Turkish government doubled the number of soldiers stationed at the tomb to 30, while Prime Minister Erdoğan warned that "the tomb of Suleyman Shah and the land that surrounds it are Turkish territory. Any act of aggression against it would be an attack on our territory and NATO territory." In February 2015, the army launched a raid
into Syria in order to move the tomb closer to the border.
Until September 2014, Turkey did not overtly participate in the international airstrikes
Turkey had repeatedly said it wanted the US to focus its air strikes in Syria as much on removing Assad as on fighting the ISIL; it had also demanded a "safe zone" in the area extending from the Syrian town of Kobanî
on the Turkish border, westward to the town of Azaz
, that would be protected by air power and that was purported to enable Turkey to transfer back to Syria some of an estimated 1.8 million displaced people camped on Turkish territory.
In October 2014, U.S. Vice President Joe Biden
stated that Turkey
, Saudi Arabia
and the United Arab Emirates
had "poured hundreds of millions of dollars and tens of thousands of tons of weapons into anyone who would fight against Al-Assad, except that the people who were being supplied were al-Nusra
, and al Qaeda
, and the extremist elements of jihadis
coming from other parts of the world."
On 22 July 2015, Turkey agreed to let the US use the Incirlik Air Base
in southern Turkey to launch air attacks against the ISIL, a deal that was seen as a major shift in policy on the part of the once-reluctant American ally
(in March 2003, the Turkish parliament voted against allowing Turkey to be a base of operations for the U.S. invasion
At the end of July 2015, American and Turkish media outlets reported that the US government and Turkey had agreed on the outlines of a de facto "safe zone" along the Turkey-Syria border under the terms of a deal that was purported to increase the scope and pace of the U.S.-led air missions against the ISIL in northern Syria; the plan provided for driving ISIL, the al-Nusra Front
, and other radical groups out of a 68-mile-long area west of the Euphrates River and reaching into the province of Aleppo that would then come under the control of the Syrian opposition.
The operational status of the envisioned area was to stop short of meeting Turkish demands for a full-scale, declared no-fly zone.
In August 2015, the US announced it would withdraw two Patriot missile-defense
batteries from southern Turkey in the autumn that year;
also withdrawn were the German Patriots stationed in Turkey,
amidst concerns in the NATO military establishment that Turkey was intent on dragging NATO into the Syrian conflict.
In late July 2015, the outlawed PKK
, designated as a terrorist organization by UN, EU and many countries including USA as well as Turkey, resumed fighting
against the government in the Kurdish-dominated southeastern parts of Turkey. On 29 June 2015, Turkey′s National Security Council made a decision and released a statement that said that Turkey would consider any incursion west of the Euphrates in northern Syria along the Turkish border (the area between Jarablus
in the east and the Azaz
region in the west) by Kurdish YPG militia, backed by the Democratic Union Party (PYD)
, as well as any attack north of Idlib by Syrian government forces to be a violation of the “red line.”
(The PYD is deemed by Turkey to be the Syrian affiliate of PKK, but it is actively aided by the U.S.
) At the end of October 2015, Turkish prime minister Ahmet Davutoğlu
claimed that Turkey had struck Kurdish YPG militia fighters in Syria twice for the alleged breach of the "red line"; the YPG′s statements said that the Turkish army had twice attacked its positions near the border towns of Tell Abyad
In mid-November 2015, president Recep Erdoğan reaffirmed this threat not to allow Kurdish YPG militia to cross over to the western side of the Euphrates along the Turkish border.
Turkish-occupied territory (red) and SDF
-controlled territory (green) in December 2018
On 24 November 2015, speaking shortly after the shootdown of a Russian Su-24
by Turkey, Russian president Vladimir Putin
characterised the role played by Turkey in the Syrian conflict as that of "the accomplices of terrorists."
Russia′s foreign minister Sergey Lavrov
claimed that the Turkish plan to create a buffer zone in the area where Syrian Turkmen
lived in northern Syria stemmed from Ankara's wish "to protect local terrorist infrastructure." 
Many Turkish and Western analysts as well as officials questioned that ISIL oil was being imported into Turkey, argued that Moscow′s accusations of the Turkish government in this regard were unfounded.
In late November 2015, following Russian President Putin
directly accusing Turkey of aiding ISIL and al-Qaeda, Turkey came under pressure from the US to close the remaining crossing point for ISIL militants on a 60-mile stretch of the border with Syria where ISIL had control of the Syrian side.
On 2 December 2015, Russia′s military officials presented what they referred to as "only part of the available facts" that proved that Turkey′s president Recep Erdogan and his family were personally involved in a multimillion-dollar oil smuggling operation that funded ISIL terrorists.
The accusations were seen as further drastic escalation of tensions between Turkey and Russia that has its military personnel and advanced weapons openly deployed in Syria.
Both the Turkish government and the Iraqi Kurdish Regional Government (KRG) denied this.
Commenting on the allegations, John R. Bass
, the US Ambassador to Turkey, told the press that the claims about the Turkish government's involvement in ISIL oil trade were unfounded, citing the official apology issued by the CIA with regards to the allegations in 2014.
On 24 February 2015, president Erdogan speaking on television of the tentative plan
for a cessation of hostilities in Syria announced by Russia and the US two days prior, accused the UN, the West, Russia and Iran of seeking to further their own interests in Syria and said he feared a U.S.-Russian ceasefire plan would do little more than benefit Syria′s president Bashar Assad.
In late December 2015, in an interview for Al Arabiya
Turkey′s president Recep Erdogan said, "Syria, Iran, Iraq and Russia have formed a quartet alliance in Baghdad and asked Turkey to join, but I told President [Vladimir] Putin that I cannot sit alongside a president whose legitimacy is distrustful."
After Syria′s Kurdish YPG militia captured Syria′s Menagh Airbase
and several settlements north of Aleppo near the border with Turkey, Turkey on 13 February 2016 began a sustained campaign of shelling
the YPG positions in the area of Azaz
from its territory.
In response to this action qualified by Syria as a violation of its sovereignty as well as the alleged infiltration into Syria of "Turkish soldiers or Turkish mercenaries", the Syrian government requested that the UN Security Council take action.
The attempt by Russia on 19 February 2016 to have an appropriate resolution adopted by the UN Security Council was undermined by Western powers, including the US, the UK, and France.
Since August 2016, the Turkish military have conducted a series of cross-border operations
in Syria, mainly fighting against the Kurdish YPG militia forces, supported by the U.S., that controlled the northern parts of Syria.