July 27 (Reuters) - The uprising against Syrian President Bashar al-Assad has changed the course of U.S. policy from one of engagement when President Barack Obama first took office to a call for Assad to step down to increased support for Syrian rebels.
Here are some of the significant moments.
March 7, 2009 - The United States and Syria found "common ground" when U.S. officials Jeffrey Feltman and Dan Shapiro met with Syrian Foreign Minister Walid al-Moualem in the first high-level trip by American officials to Damascus since 2005.
Feb. 16, 2010 - Obama nominated Robert Ford to be the U.S. ambassador to Syria, the first since Washington withdrew its ambassador in 2005 after the assassination of former Lebanese Prime Minister Rafik al-Hariri in Beirut.
Feb. 17, 2010 - Assad held security talks in Damascus with U.S. Under Secretary of State William Burns, after which the U.S. official said he was "hopeful" of progress.
April 8, 2011 - In a statement on the uprising, which began on March 15, Obama called on Assad to halt the "abhorrent violence committed against peaceful protesters."
April 22, 2011 - Obama condemned use of force against demonstrators and called on Assad to "change course now."
April 29, 2011 - United States slaps sanctions on Syria's intelligence agency and two relatives of Assad, in Washington's first concrete steps in response to the crackdown on protests.
July 12, 2011 - Obama sharpened rhetoric against Assad, saying the Syrian president had "lost legitimacy" for failing to lead a democratic transition.
Aug. 11, 2011 - Obama and Turkish Prime Minister Tayyip Erdogan in a phone call spoke about the violence in Syria and the need for a transition to democracy, the White House said.
Aug. 18, 2011 - For the first time, Obama called for Assad to step down, saying: "For the sake of the Syrian people, the time has come for President Assad to step aside." Britain, France and Germany also called for Assad to step aside.
Oct. 24, 2011 - The United States pulled its ambassador, Robert Ford, out of Syria over threats to his safety.
May 18, 2012 - Group of Eight leaders at Camp David discussed the need for political transition in Syria.
June 18, 2012 - Obama and Russian President Vladimir Putin at the Group of 20 summit in Mexico agreed violence in Syria must end but showed no signs of reaching a deal on tougher sanctions against Damascus.
June 22, 2012 - U.S. Defense Secretary Leon Panetta defended the administration's decision to not arm the Syrian rebels, which has been criticized by some Republicans in Congress.
July 18, 2012 - Obama called Putin to discuss the deteriorating situation in Syria after a bombing in Damascus killed members of Assad's inner circle, but the two leaders ended the call divided over the best way forward.
July 19, 2012 - U.S. Ambassador to the United Nations Susan Rice called the Russian and Chinese vetoes of a U.N. Security Council resolution on Syria "dangerous and deplorable."
July 23, 2012 - Obama says Assad will be held accountable if he makes the "tragic mistake" of using Syria's stockpile of chemical weapons. (Reporting by Lauren French; Editing by Stacey Joyce)