Washington• 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."
"The use of chemical weapons would be a game changer," Obama told reporters. "When you use these kinds of weapons, you have the potential of killing massive numbers of people in the most inhumane way possible, and the proliferation risks are so significant that we don't want that genie out of the bottle."
But the administration also has said the intelligence reports citing physical evidence of chemical weapons use were not certain enough to cross Obama's stated "red line," which he said last summer would have "enormous consequences."
Obama said Friday in Costa Rica that "we have evidence that chemical weapons have been used. We don't know when, where, or how they were used." A U.S. investigation, he said, will help "get a better handle on the facts."
"When it comes to using chemical weapons, the entire world should be concerned," he added.
Arming the rebels is the most likely escalation, officials said. Even the most ardent advocates of U.S. intervention don't want American military boots on the ground. A no-fly zone would demand an intensive operation to neutralize Syria's Russian-supplied air defenses. Officials said targeted strikes are likely to be considered only after uncontested proof emerges of chemical weapons use or the intelligence suggests repeat attacks may be imminent.
Any U.S. military action, including arming the rebels, would be weeks away, officials said. They stressed that a strategy would first have to be coordinated with several important allies to ensure that the right weapons get to the right forces and that donors aren't duplicating efforts. The U.S. also would try to secure contributions from more Arab and European partners, they said, while continuing to check rebel brigades that are untainted by al-Qaida or other extremists who've joined the anti-Assad fight.
The range of reservations to direct military intervention explains why the administration is putting great stock in a unified international approach. Swaying Russia would remove an important consideration for many potential coalition partners and leave Assad with only Iran and the Lebanese militant group Hezbollah as reliable allies.
It would eliminate the possibility of a Russian veto to any future request for U.N. authorization to directly intervene in Syria.
Obama never has said he must have a U.N. mandate to act, but U.S. officials repeatedly have cited it as one explanation for why the American response in Syria hasn't been more forceful. Also, no one in the United States wants a repeat of the diplomatic humiliation suffered by President George W. Bush in the runup to the 2003 Iraq war.
The chances for a Russian shift are unclear. U.S.-Russian relations are mired in disputes from missile defense in Europe to adoptions and new Russian laws against political dissent. Arguments outlining the costs of increased international criticism for remaining steadfast in support of the Assad government have repeatedly failed to move Moscow.
Officials say Kerry is optimistic he can sway Putin; others are more skeptical.
At a minimum, officials said, reaching out to Russia could pre-empt arguments that the U.S. is moving toward military options in Syria without giving diplomacy a final chance.
Gaining even Russia's grudging acquiescence in private to greater American involvement in Syria, as with NATO's Kosovo intervention in the 1990s, could be viewed as a critical if silent diplomatic victory for the United States.