There had been no expectation that Obama was ready to lift the measures, but the renewal comes at an especially sensitive time in US-Syria relations, despite efforts by the administration to return an ambassador to Damascus.

Obama said in a message to Congress renewing the sanctions imposed by former president George W. Bush in 2004, that the Syrian government had made "some progress" in suppressing the infiltration of foreign fighters bound for Iraq.

But he added that its "continuing support for terrorist organizations and pursuit of weapons of mass destruction and missile programs, continue to pose an unusual and extraordinary threat to the national security, foreign policy, and economy of the United States."

Obama also called in Syria to demonstrate "progress" in the areas that Washington says justifies sanctions, to allow them to be lifted in future.

US-Syrian ties had been gradually improving. But tensions have risen with the United States accusing Syria of sending weapons to the Iranian-backed Hezbollah that Washington says could lead to a new war in the Middle East. Syria has denied the allegations.