WASHINGTON (AP) -- The Obama administration is trying to leverage new evidence that Syrian President Bashar Assad's government used chemical weapons, and make a fresh diplomatic and possible military push with allies to end the country's civil war.
This renewed effort starts with Secretary of State John Kerry's trip to Moscow this coming week for talks with leaders in Russia, the Syrian government's most powerful international friend.
Russia, alongside China, has blocked U.S.-led efforts three times at the United Nations to pressure Assad into stepping down. The U.S. hopes to change Moscow's thinking with two new arguments, officials said: the evidence of chemical weapons attacks and, with the war now in its third year, American threats to arm the Syrian rebels.
Russia represents the most difficult diplomatic test as the U.S. tries to assemble a global coalition to halt a war that has claimed more than 70,000 lives.
Washington wants a peaceful resolution and sees U.N.-imposed sanctions against Syria as an effective tool for pressuring Assad into negotiations. With Assad's government unwilling to talk with the opposition, and Russia providing military and diplomatic backing, hopes of a negotiated transition are all but dead for now.
The stalemate and the risk of greater chemical weapons usage are driving President Barack Obama to explore new options, including military ones. But, he made clear Friday during a visit to Costa Rica, "I do not foresee a scenario in which boots on the ground in Syria, American boots on the ground, would not only be good for America but also would be good for Syria."
Obama said at a Washington news conference earlier in the week that any new U.S. action should be taken prudently and in concert with international partners. Two days later, Defense Secretary Chuck Hagel said arming the Syrian opposition was a policy consideration.
Kerry's departure Monday for Russia sets the stage for some critical discussions.
In Moscow, officials said Kerry will attempt to persuade Russian President Vladimir Putin to support, or at least not veto, a fresh effort to impose U.N. penalties on Syria if Assad doesn't begin political transition talks with the opposition.
To make his case, Kerry will present the Russians with evidence of chemical weapons use and relay the Obama administration's readiness to give weapons to the Syrian rebels, according to the officials, who demanded anonymity because they weren't authorized to speak publicly about the confidential diplomacy.
Although the U.S. is prepared to act with or without the Russians' help, officials say a coordinated effort to end the war would be much easier with Moscow on board.
China is seen as largely following Russia's lead.
The U.S. also wants Russia, which maintains a naval base in Syria, to stop honoring existing contracts with the Assad government for defense hardware and to refrain from doing anything else to bolster his forces.
Unlike with Afghanistan and Iraq, several of America's Western and Arab allies are significantly ahead of the United States in their readiness to intervene in Syria.
Just on Friday, an Israeli airstrike against Syria targeted a shipment of advanced missiles believed bound for the Lebanese military group Hezbollah, Israeli officials said Saturday. The officials said the attack was aimed at sophisticated "game-changing" weapons, but not chemical arms.
Saudi Arabia and Qatar have provided the rebels with advanced weaponry. Turkey has given the opposition leadership a home base and significant logistical support. Britain and France have ramped up support ahead of the U.S. at almost every step.
Somewhat similar to the Libya intervention two years ago, Washington is being pulled by several of its closest partners into an ambivalent escalation in Syria.
As the U.S. extricates itself from a decade of fighting in the Muslim world, it has been reluctant to get involved in a new conflict colored by sectarian warfare and terrorist groups engaged on both sides of the battle.
The U.S. also notes that the Syrian government has far greater defensive capacities than those of Libyan dictator Moammar Gadhafi, whose military was easily eliminated in 2011.
But the rising death toll, increased international clamoring for greater American leadership and the threat of weapons of mass destruction proliferation in the heart of the Middle East, between Iraq and Lebanon and bordering Israel, have led Obama to reassess his options.
Obama this past week reaffirmed his view that the "only way to bring stability and peace to Syria is going to be for Assad to step down." Even before the reports of chemical weapons use, he said, the U.S. sought to strengthen Syria's opposition. Now, however, "some options that we might not otherwise exercise ... we would strongly consider."