US involvement in Syria since 2011

Washington (AFP) - The United States Friday announced it was deploying special forces to Syria, relenting on a long-standing refusal to put US boots on the ground and deepening the fight against the Islamic State group.

Here is a history of Washington's involvement in the four-year-old conflict.

- Pressure on Assad -

April 29, 2011: Washington responds to a bloody crackdown on protests by slapping sanctions and asset freezes on Syrian regime figures including the powerful brother of President Bashar al-Assad, Maher.

May 19, 2011: US President Barack Obama calls on Assad to lead a political transition in Syria, or step aside. A day earlier Washington ordered the first direct sanctions against Assad himself.

July 8, 2011: The US ambassador in Damascus, Robert Ford, challenges the Syrian regime by traveling to Hama, a central city besieged by the army and scene of a massive demonstration against Assad.

August 18, 2011: Obama and his Western allies for the first time call explicitly on Assad to stand down.

October 24, 2011: The United States announces that its ambassador has left Syria for security reasons. Damascus recalls its ambassador from Washington. In the next two years Ford shuttles between the United States and Turkey many times, spending hours with leaders of the Syrian opposition installed near Istanbul.

- Diplomatic efforts -

June 30, 2012: In Geneva a so-called action group, made up of the United States, Britain, China, France, Russia, Turkey and Arab states, agrees on a plan for a political transition in Syria -- but fails to reach a consensus on Assad's removal. Washington says the plan marks the start of a "post-Assad" period, while Beijing and Moscow maintain it is up to Syrians to determine their future.

September 14, 2013: Following an August 21 chemical weapons attack attributed to Assad's regime, Russia and the United States agree to dismantle Syria's chemical weapons arsenal -- averting at the last moment the threat of a US military strike.

January 22-February 15, 2014: Syrian government and opposition figures hold talks in Switzerland, under pressure from Russia and the United States, but the negotiations end in failure with Washington blaming "obstruction" by the Syrian regime.

- Military action -

August and September 2013: Obama promises, on half a dozen occasions, that he will not put American boots on the ground in Syria. Instead, the United States soon begins a program to train and equip Syrian rebels fighting Assad.

September 23, 2014: The United States and Arab allies launch air strikes in Syria targeting the Islamic State (IS) group, which emerged from the civil war as the strongest group fighting the regime. The strikes expand the US-led campaign against the extremist rebels in neighboring Iraq.

September 30, 2015: Russia's air force carries out its first air strikes on Syria. Moscow claims to have hit IS targets, but Washington accuses it of targeting moderate rebel group to shore up Assad's regime.

October 9, 2015: The Pentagon pulls the plug on a troubled program to create Syrian rebel units to fight IS, nine months after its launch.

October 30, 2015: Washington approves the deployment of up to 50 special operations forces in Syria to assist the anti-jihadist fight. The White House insists US strategy has not changed, despite a move widely seen as contradicting Obama's "no boots on the ground" policy.