President Obama should "state unequivocally" that Syrian leader Bashar al-Assad should step down from power, Sens. John McCain (R-Ariz.), Lindsey Graham (R-S.C.) and Joe Lieberman (I-Conn.) said Thursday.

The trio ramped up pressure on Obama to take a stronger stance against the Assad regime, which has violently cracked down on anti-government protesters demanding reforms.

"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," the senators said in a statement, referring to the leaders of Libya and Egypt. "The President should take tangible diplomatic and economic measures to isolate and pressure the Assad regime, including through targeted sanctions against Assad himself and other regime officials who are responsible for gross human rights abuses."

The administration took part in airstrikes against Libyan leader Moammar Gadhafi's regime, and pressured Hosni Mubarak to step down as Egypt's president. 

The administration has been sharply critical of the Syrian government's crackdown against protesters, and White House press secretary Jay Carney said Wednesday that the president was considering a variety of options to punish the Assad government.

"What I would tell you is that, as I did yesterday, we’re pursuing a range of possible policy options, including targeted sanctions, to respond to the crackdown and make clear that this behavior by the Syrian government is unacceptable," Carney said. "We strongly oppose the Syrian government’s treatment of its citizens and we continue to oppose its continued destabilizing behavior, including support for terrorism and terrorist groups. We call on President Assad to change course now and heed the calls of his own people."

Obama has faced criticism from lawmakers in both parties for his administration's response to a similar situation in Libya, in which the U.S. joined NATO forces to launch targeted military strikes against Gadhafi. But the administration's been loath to add military might to back other efforts to overthrow longstanding leaders in the region.

McCain, who toured the region, including Libya, in the past week, has said he doesn't favor military action in the region.