WASHINGTON — US Secretary of State Hillary Clinton on Friday urged countries to stop trading with Syria as she sought to step up the pressure on President Bashar al-Assad to end a brutal crackdown on protesters.

"We urge those countries still buying Syrian oil and gas, those countries still sending Assad weapons, those countries whose political and economic support give him comfort in his brutality, to get on the right side of history," Clinton told reporters.

In an interview with CBS on Thursday, the chief US diplomat urged China and India as well as European nations to impose energy sanctions on Syria and urged Russia to abandon its decades-long practice of selling arms to Damascus.

"President Assad has lost the legitimacy to lead and it is clear that Syria would be better off without him," Clinton told a Washington press conference Friday alongside visiting Norwegian Foreign Minister Jonas Gahr Stoere.

But Clinton stopped short of explicitly calling on Assad to step down -- a call US officials say President Barack Obama's administration has decided to make and will come in the following days.

Asked by CBS News why Washington had not already urged Assad to go, Clinton replied: "it?s important that it?s not just the American voice. And we want to make sure those voices are coming from around the world."

The United States is being careful to promote a broad international response "so that there will not be any temptation on the part of anyone inside the Assad regime to claim that it's only the United States" or the West leading the campaign against Damascus, she said Friday, adding: "Indeed, it's the entire world."

Clinton also said that the US ambassador to Damascus, Robert Ford, had delivered a "clear message" to the Syrian government, alluding to his meeting Thursday with Syrian Foreign Minister Walid Muallem.

"Immediately stop the violence, withdraw your security forces, respond to the legitimate aspirations of the Syrian people for a democratic transition in concrete and meaningful ways," she said, reading out the message.

The Syrian Observatory for Human Rights says a total of 2,150 people have been confirmed dead since protests against the Assad family's four-decade grip on power erupted mid-March.

Syrian security forces opened fire again on Friday killing at least 10 people as thousands of anti-regime protesters rallied in flashpoint cities after weekly prayers, rights activists said.