Relations between erstwhile allies Turkey and Syria, which share a long border, have soured since the revolt broke out against Syrian President Bashar al-Assad's regime in March 2011.
Turkey is now home to an estimated 400,000 refugees and harbours many of the Syrian opposition's top civilian and military leaders.
At least 40 people were killed Saturday in twin car bomb blasts in the border town of Reyhanli, the worst such attack since the start of the conflict. Ankara said it suspected Damascus.
- April 29, 2011: The first Syrian refugees fleeing the violence arrive in southern Turkey.
- September 21: Turkish Prime Minister Recep Tayyip Erdogan says Ankara has broken off contacts with the Syrian regime, which he previously accused of committing "atrocities" in putting down the revolt.
- October 2: Syrian opposition leaders meeting in Istanbul announce the creation of a broad-based Syrian National Council.
- October 4: The Turkish news agency Anatolia says Colonel Riyadh al-Asaad, who defected from Syria's army in July, has set up a Free Syrian Army operating out of Turkey.
- November 15: Turkey imposes its first sanctions on Damascus, halting oil exploration in Syria.
- November 30: Turkey says it is cutting trade relations with Syria.
- April 9: The Syrian Observatory for Human Rights, a Britain-based monitoring group, says Damascus regime forces have fired across the border at refugee camps in Turkey.
- June 22: Syrian anti-aircraft gunners shoot down a Turkish warplane near the border.
- Sept 19: Three civilians in the southeastern town of Akcakale are wounded by stray bullets fired from the Syrian border post of Tal-Abyad as rebels clash with regime forces.
- October 3: Syrian shells hit Akcakale, killing five people, the first time Turks have been killed by cross-border fire. Turkey shells Syrian targets in response.
- October 4: Turkey continues to hammer Syrian targets, as parliament authorises military operations against targets in Syria.
- October 10: Turkish jets force a Syrian airliner flying from Moscow to land in Ankara on suspicion it is carrying weapons.
- October 11: Syria has stopped buying electricity from Turkey, Turkish Energy Minister Taner Yildiz says.
- October 12: Russia says the intercepted plane was carrying a cargo of dual-purpose radar equipment and insists it did not violate any laws.
- January 26: The first of six batteries of Patriot missiles deployed by NATO on the Turkish border is declared operational.
- February 11: A car bomb attack blamed by Ankara on the Syrian intelligence services kills 17 people at the Cilvegozu border post. Four Syrians and a Turk suspected over the bombing are detained the following month.
- May 2: A Turkish policeman is killed in Akcakale by shots believed to have been fired from the Syrian side of the border.
- May 11: Two explosive-laden cars blow up in the border town of Reyhanli, killing 40 and leaving around 100 wounded, according to the interior ministry. Ankara said it suspected Damascus' involvement. A third explosion later rocks the town.