President Obama on Monday pressed Russian President Vladi­mir Putin to join the United States and its allies in a campaign to force Syria’s ruling party out of power, as a means to end 15 months of escalating bloodshed.

In their first meeting as heads of state, the two leaders spent about one-third of a two-hour discussion on the crisis in Syria, a dialogue that Obama called “candid and thoughtful.” But there was little immediate evidence that the Russian leader would end his support of Bashar al-Assad, whose brutal crackdown on his own people has outraged the international community.

“We agreed that we need to see a cessation of the violence, that a political process has to be created to prevent civil war,” Obama said in brief remarks to reporters after the meeting.

Obama called the violence “horrific,” and added that he and Putin agreed to work with the United Nations, mediator Kofi Annan and other “international actors” to find a resolution.

Putin said that he and Obama found “many commonalities” on a range of issues and now will “further develop our contacts both on a personal level and on the level of our experts involved.”

The meeting, held on the sidelines of the Group of 20 economic summit, came just days after Secretary of State Hillary Rodham Clinton accused Russia of causing a “dramatic escalation” of the crisis in Syria by shipping helicopters to the regime there. She later backtracked, saying the helicopters had merely been in Russia for routine repairs.

Three weeks ago, the United States and 10 other countries expelled Syrian diplomats following the massacre of more than 100 people in the Syrian village of Houla.

Administration officials described Obama’s conversation with Putin as fruitful, with the two leaders also discussing Iran, bilateral trade and missile defense. But it was Syria that dominated the talk.

The Russian president agreed that a “political process” must be established in Syria to prepare for a democratic government, even though he did not directly address Assad’s future, the White House aides said.

While Obama emphasized that Assad must go, Putin pursued “a bigger discussion,” said Michael McFaul, the U.S. ambassador to Russia.

The Russians “want to talk about what happens the day after” a transition, explained McFaul, who was at the meeting. “They want to broaden our aperture. The Russians want to remind us that the day after the fall of a leader, the political transition, the political process goes on.”

McFaul added that the meeting lasted so long because the presidents “didn’t want to stop talking about Syria. Both leaders want to make sure the leader on the other side of the table understands each other’s motivations.”

Reporters allowed into the room described Putin as leaning away from Obama when he spoke and avoiding eye contact. The two have had a frosty relationship since the only other time they met, in 2009 when Obama traveled to Russia and Putin was prime minister.

Despite the Obama administration’s desire to “reset” the U.S.-Russia relationship, Putin did not attend the Group of Eight summit at Camp David last month, and Obama will not go to an Asian economic summit scheduled in Russia this fall.

White House aides, however, cautioned reporters not to read too much into Putin’s body language, saying he is not as expressive as his predecessor, Dmitry Medvedev, who developed a friendship with Obama.

“The chemistry was very business-like, cordial,” McFaul said. “I’ve been to a lot of meetings with Putin, watched lots of video of him, and there was nothing extraordinary about him today. That’s what he looks like, the way he acts.”

Obama’s discussion with Putin came as the president prepared for two days of meetings with world leaders that were expected to focus largely on the European debt crisis.

Obama hailed Sunday’s Greek election results as a “positive prospect” and called on his counterparts to “avoid protectionism” as they seek to stabilize the global economy.

Obama said the victory of Greek politician Antonis Samaras, whose New Democracy party has endorsed the bailout package that is keeping Greece afloat, would allow the country’s leaders to work “constructively with their international partners in order that they can continue on the path of reform and do so in a way that also offers the prospects for the Greek people to succeed and prosper.”

Speaking after a morning meeting with Mexican President Felipe Calderon, Obama cautioned that “the world is concerned about the slowing of growth that has taken place.”

“Now is the time, as we’ve discussed, to make sure that all of us join to do what’s necessary to stabilize the world financial system, to avoid protectionism, to ensure that we are working hand-in-hand to both grow the economy and create jobs,” he added.

Obama entered the summit with hopes of cementing international support behind a mixture of stimulus spending to spark growth and fiscal consolidation for countries struggling with high debt. The European debt crisis has contributed to U.S. economic sluggishness, which has threatened to make Obama’s path to reelection more difficult.

After talking with Putin, Obama met with German Chancellor Angela Merkel, who has championed fiscal austerity for Europe. White House spokesman Jay Carney said Obama “was encouraged by what he heard about the ongoing discussions in Europe on paths they’re pursuing to address the crisis.”

Calderon thanked Obama for his executive action Friday to stop the deportation of some illegal immigrants who came to the United States as children.

Calderon called the move “unprecedented” and said it took “valor and courage.”