The US is stepping up pressure on the regime in Damascus, targeting Syrian president Bashar al Assad personally with sanctions over human rights abuses.
Assets belonging to Assad and six other senior figures will be frozen – although it is thought these may have more a symbolic than practical impact.
The measures come amid reports that Syrian tanks have been shelling the town of Tel Kelakh for the fourth day.
New videos have appeared on social media websites claiming to show recent anti-government demonstrations. Their authenticity cannot be verified.
Some of the pictures are said to illustrate the effect of a strike in the city of Homs, with shops closed in response to calls to defy the regime.
Despite a severe security crackdown involving reported mass arrests, new protests are said to have sprung up.
The latest move from Washington targeting Assad directly follows sanctions imposed by the US and the EU on other top Syrian officials.
President Obama says the measures are a response to the “continuous escalation of violence against the people of Syria”.
The US hopes the EU among others will follow suit. European governments are to decide next week whether to target Assad directly.
The American move comes a day before President Obama is due to make a major speech on the uprisings in the Arab world.