Secretary of State Hillary Clinton, facing resistance from Russia, appealed to the United Nations Tuesday to support an Arab League-backed resolution that calls for Syrian President Bashar Assad to step down. 

In a forceful plea at a meeting of the U.N. Security Council, Clinton voiced confidence in the prospects for a political transition in Syria. But she suggested the death toll would rise considerably if the international community does not apply more pressure soon. 

"We all know that change is coming to Syria. Despite its ruthless tactics, the Assad regime's reign of terror will end and the people of Syria will have a chance to chart their own destiny," she said. "The question for us is how many more innocent civilians will die before this country is able to move forward." 

Clinton said nations have a choice -- "stand with the people of Syria and the region or become complicit to the continuing violence there." 

More than 5,000 people have died since the Syrian uprising began last March, nearly 100 on Monday alone. Clinton said "the evidence is clear that Assad's forces are initiating nearly all of the attacks that kill civilians," though she warned violence could "spiral out of control" as more Syrians take up arms. She warned about a possible "descent into civil war." 

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But Clinton is facing pushback at the United Nations from Russia. While the Arab League-backed resolution calls for an end to violence and threatens "further measures" if Assad does not step down, Russia describes that as a path to civil war, or worse. 

"We are going to witness a very bad situation, much, much, much broader than just Syria or Libya or Egypt or any other single country," Russian foreign minister Sergei Lavrov said. 

The Russians enabled military action in Libya by abstaining on the Security Council resolution that authorized it. They now consider that a mistake they won't make in strategically important Syria, which is their last Arab ally. 

Clinton on Tuesday said an attempt to liken the Syrian conflict to the war in Libya is a "false analogy." Clinton said Syria is unique, and that the Arab League proposal would provide a path for "political transition" while preserving the state's institutions. 

"It deserves a chance to work," Clinton said of the plan. "This will be hard, the results are far from certain, success is far from guaranteed. But the alternative, more of Assad's brutal rule, is no alternative at all." 

The U.S. has been trying to convince Russia that Assad will eventually go and that the leadership that replaces him won't like countries that prolonged the Syrian people's suffering. 

But officials admit the timing of such a transition is unclear. "I personally believe it's a question of time before Assad falls, but that's the issue, it could be a long time," Director of National Intelligence James Clapper said Tuesday on Capitol Hill

And the U.S. apparently has had a tough time connecting with Russia. State Department spokesman Mark Toner said Tuesday that Clinton has tried to reach Lavrov, but he hasn't called back. 

"There's nothing more substantial and more pressing in international affairs right now than the situation in Syria," Toner said. 

Some say the Obama administration should force Russia to choose between Assad and the Syrian people -- by forcing Moscow to either veto the resolution or not. 

"If you don't have a vote, you signal to the Arab world and to the Syrians in particular, that the U.N., the international community and, more importantly, the United States doesn't care about the opposition in the street," said Richard Grenell, former U.S. spokesman at the United Nations under the George W. Bush administration. 

"It's time for Moscow to understand that not even the Russian winter can freeze Syria's Arab Spring," Hillel Neuer, executive director of UN Watch, said in a statement. "Instead of its increasingly futile effort to shield the doomed Assad regime, Russia would (do) better to prepare the dictator's Moscow asylum, something he will need sooner rather than later." 

Fox News' Wendell Goler contributed to this report.