Administration officials continue to offer "empty words of scorn and condemnation ... hollow pledges that the killing must stop [and] more strained expressions of amazement at what has become so tragically commonplace," McCain said of the violent oppression of anti-government forces by Syrian president Bashar Assad.

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"When regimes are willing to commit any atrocity to stay in power, diplomacy cannot succeed until the military balance of power changes on the ground," he added.

Lieberman compared the growing massacre of Syrian civilians at the hands of Assad's forces to Balkan wars of the 1990s, which resulted in the worst atrocities since World War II.

The Obama administration's message to "to victims of this brutal violence [is] essentially words of sympathy," according to Lieberman. However, those words "don't stand up against Assad's tanks," he added.

The White House in May floated a tentative plan that would have Washington and Moscow ease Assad out of office while allowing a number of his top officials to remain in government.

A similar plan was used to push out former Yemeni president Ali Abdullah Saleh in the wake of the Arab Spring movement.

However, McCain told fellow senators that a Syrian peace strategy that hinges upon support from Moscow is basically a nonstarter.

"U.S. policy in Syria now seems to be subject to the approval of Russian leaders who are arming Assad’s forces," McCain said Thursday on the Senate floor.

"Meanwhile, the [White House] refuses even to provide weapons to Syrians who are struggling and dying in an unfair fight, all for far of militarizing the conflict," he added.

The death and carnage on the streets of Homs and Houla is evidence enough that the conflict is already militarized, Lieberman said.

The White House and Pentagon have acknowledged that a peace plan spearheaded by U.N.-Arab League envoy Kofi Annan has basically failed.

"There is no justification for this regime’s continued defiance of its obligations under the [U.N. peace plan], and Assad’s continued abdication of responsibility for these horrific acts has no credibility and only further underscores the illegitimate and immoral nature of his rule," White House spokesman Jay Carney said in statement issued Thursday.

"We call once more on all nations to abandon support for this brutal and illegitimate regime, and to join together to support a political transition in Syria," he added.

But Russia's waffling support on the U.N. Security Council for an alternative peace plan only adds more doubt on whether Moscow will back efforts to move Assad out of power or if it will continue "to protect its ally in Damascus," Lieberman said.

To that end, allowing U.S. and allied airstrikes against key targets inside Syria would "break the will" of pro-Assad forces and "result in a much sooner end to this terrible waste of life," Lieberman said.

But Russian Deputy Foreign Minister Gennady Gatilov reiterated the country's opposition to any international action against the Assad government. Any external effort to oust Assad by force "will only exacerbate the situation for both Syria and the region as a whole," he told reporters on May 30.



