The U.S. and Russia agreed Tuesday to try to convene an international conference this month to come to a political solution to end the two-year Syrian civil war but gave no indication how they would convince President Bashar Assad into talks with the rebels seeking to overthrow him.

Secretary of State John Kerry said that if such a gambit were successful, it might no longer be necessary to consider arming the Syrian rebels. Kerry also said it was up to the Syrian people whether Assad should leave office.

Yet even as Kerry and Russian Foreign Minister Sergey Lavrov hailed their joint strategy as evidence of enhanced U.S.-Russian cooperation, it was unclear how their plan might work toward ending a war that has become even more dangerous in recent months with accusations the Assad regime has used chemical weapons, Israeli airstrikes on weapons convoys and American threats to begin arming the rebels.

"Despite different points of view, committed partners can accomplish great things together when the world needs it," Kerry told reporters in Russia's capital. "And this is one of those moments."

The outcome of more than five hours of meetings in Moscow involving President Vladimir Putin, Kerry and Lavrov essentially bring diplomatic efforts to halt Syria's violence to a point they were about a year ago. The former Cold War foes, who've split bitterly over how to halt the conflict, said they'd work to revive a transition plan they laid out in June 2012 but which never gained momentum with Syria's government or the opposition. They said this time they were committed to bringing the Syrian government and rebels to the negotiating table.

Speaking about the U.S. strategy, Kerry suggested the Obama administration would consider holding off on any possible plan to provide weapons to vetted units of the Syrian opposition if a peace strategy takes hold.

Kerry said the final proof of whether Assad's forces used chemical weapons in two attacks in March, as suggested last week by a U.S. intelligence assessment, would go a long way toward determining what course of action Obama takes. Talking about the U.S.-Russian peace strategy's effect on decision-making, he said, "much will depend on what happens over the course of these next weeks."

That appeared to be a minor concession to Russia, which has argued vehemently against any foreign governments providing military assistance for fear it would aid extremists. It could also reflect the Obama administration's continued discomfort with the greater involvement in Syria, where it has expressed deep reservations over most of the military options currently being considered.

Kerry also appeared to back down from the outright U.S. demand that Assad step down in the transition, while maintaining that he, personally, couldn't see how a leader responsible for such widespread abuses could remain in power as part of a peace deal.

"But I'm not going to make that judgment," he said, saying it was up to the Syrian people.

Kerry's statements about arming the rebels and whether Assad should go seemed at odds with statements by President Barack Obama and other Cabinet members such as Defense Secretary Chuck Hagel, who said the administration was considering arming the rebels.The White House had no comment on Kerry's remarks, except to say that U.S. policy was still that Assad must leave office.

More than 70,000 people have died in the conflict since March 2011, according to the United Nations.

Kerry said the international plan for a transition agreed to last year in Geneva must be the roadmap for peace.

"It should not be a forgotten communique of diplomacy," he said.

The Geneva plan allowed each side to veto candidates it found unacceptable for an interim government. The plan never got off the ground, though Washington and Moscow differ over the reasons.

Speaking to reporters at a government guesthouse in Moscow, Lavrov praised the Assad regime for expressing its willingness to work on a political transition and its decision to establish a dialogue with all Syrians. He said the opposition, by contrast, "hasn't said a single word yet which would show their commitment."

"When we hear the right words from the opposition, given the fact that the regime has already voiced the right words, then we will try to convert such words into actions," Lavrov said.

Kerry took a different view.

He said the alternative to the political transition strategy was more violence, a Syria that "heads increasingly toward an abyss, a worse humanitarian crisis and possibly even ethnic cleansing and the breakup of the Syrian state. He said the opposition supports the peace plan and the transition strategy and that it was up to the government to make good on its obligations, also as they pertain to not using chemical weapons.

Lavrov also expressed concerns about chemical weapons' use, but stressed the need for clear facts before any course of action is rashly decided upon. He said the two countries would boost intelligence sharing on the chemical weapons issue and that the diplomacy would continue between Obama and Putin on the sidelines of next month's Group of Eight industrialized countries' summit in Northern Ireland. Obama also plans to visit Russia later this year.

Neither official spoke about Israel's actions in recent days, which have included airstrikes on what the Jewish state says were weapons being readied for transfer to the Lebanese militant group Hezbollah. Israel's increased involvement has created new complications for all actors in the war, given its long history of conflict with much of the Arab world.