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President Obama is facing increased pressure to call for the ouster of Syrian President Bashar Assad, as Assad's government continues a violent crackdown on protesters that activists say has killed more than 450 people.

While Obama has resisted those calls so far, on Friday he imposed financial penalties against three top Syrian officials, Syria's intelligence agency and Iran's Revolutionary Guard.

"We call on President Assad to change course now, and heed the calls of his own people," the White House said Friday evening in its strongest statement yet on the unrest in Syria, calling the Syrian government's actions "deplorable."

But Sens. John McCain, R-Ariz., Lindsey Graham, R-S.C., and Joe Lieberman, I-Conn., said Thursday that Assad's government has "lost the legitimacy to remain in power in Syria."

"We urge President Obama to state unequivocally – as he did in the case of Qaddafi and Mubarak – that it is time for Assad to go," they said in a written statement, referring to Libyan leader Muammar al-Qaddafi, who is fighting rebels and a NATO-led coalition to hold onto power, and former Egyptian President Hosni Mubarak, who stepped down earlier this year in the face of a popular uprising.

"Bashar al Assad has been given countless chances to pursue meaningful dialogue and reform. He has squandered all of them," the three senators said. "Rather than hedging our bets or making excuses for the Assad regime, it is time for the United States, together with our allies in Europe and around the world, to align ourselves unequivocally with the Syrian people in their peaceful demand for a democratic government."

Former State Department spokesman P.J. Crowley asked Friday, "If Libya, then why not Syria?"

"As the crackdown in Syria escalates, it is increasingly difficult to distinguish Qaddafi's sins from those of Assad," he wrote in an opinion article published by The Daily Beast. "Having publicly called for Qaddafi's departure, the administration is hesitating to do the same with Assad. It shouldn't. ...

"If the United States is committed to promoting responsible, accountable, and representative government around the world, it cannot just do so where it is easy," he continued. "It should do so where it matters. If Qaddafi has forfeited his legitimacy, then Assad has as well, and the world's most powerful democracy should say so now, when it matters."

The financial sanctions the White House imposed Friday affect Maher Assad, the Syrian president's brother and commander of the Syrian Army's Fourth Armored Division, which is accused of carrying out the worst atrocities in the southern city of Daraa. Also affected are Assad cousin Atif Najib, the former head of the Political Security Directorate in Daraa Province, and intelligence chief Ali Mamluk.

"The United States strongly condemns the Syrian government's continued use of violence and intimidation against the Syrian people," the U.S. statement says. "We call upon the Syrian regime and its supporters to refrain from further acts of violence and other human rights abuses against Syrian citizens seeking to express their political aspirations."

The penalties probably will have limited direct impact because none of the targets is believed to have any significant assets in U.S. banks. But officials said the move was aimed at sending a clear message to the Syrian people that those responsible for the crackdown are going to face consequences, and no one in the Syrian leadership will be immune.

Although Assad himself is not among those mentioned Friday, officials said he could be named at a later date if the crackdown continues.

The Associated Press contributed to this report.