Despite their apparent accord on Syria, Mr. Obama and Mr. Hollande were reminded again of the limits of their ability to act, when Russia doubled down on its opposition to a United Nations resolution designed to free up desperately needed humanitarian aid for war-ravaged civilians.

Analysts say pressure on Russia, whether it comes from the U.S., France or anywhere else, will have limited impact.

That didn't stop Mr. Obama and Mr. Hollande — on a three-day U.S. visit that included an extravagant state dinner at the White House on Tuesday evening — from using the bully pulpit of a joint press conference to condemn Moscow's obstructionism and call for an end to the fighting in Syria.

"There is great unanimity among most of the Security Council on this resolution [to provide greater aid]. Russia is a holdout," Mr. Obama told a gathering of French and U.S. journalists. "And Secretary [of State John F.] Kerry and others have delivered a very direct message to the Russians that they cannot say they are concerned about the well-being of the Syrian people when there are starving civilians. ... [I]t is not just the Syrians that are responsible; the Russians, as well, if they are blocking this kind of resolution."

Mr. Hollande echoed those remarks, questioning how Russia could stand in the way of providing food, water, medicine and other supplies to the Syrian people.

"How can you object to humanitarian corridors? Why would you prevent the vote of a resolution if, in good faith, it is all about saving human lives?" he said.

As they directed criticism at Russia, athletes from the U.S., France and other nations around the world were competing in Sochi. The Olympics traditionally have led to something of a truce among nations, though there's little sign that the frayed relations between Russia and its foes have been soothed at all by the spirit of international athletic competition.

Mr. Obama, Mr. Hollande and most other Western political leaders skipped the Sochi Games. The official U.S. delegation, including a number of prominent gay Americans, was widely seen as slap at Russian legislation targeting homosexuals. Analysts on both sides saw a Russian riposte in Mr. Putin's choice of a former Olympic figure skater who publicly made a racist joke about Mr. Obama and first lady Michelle Obama to help light the torch in Sochi.

As the civil war worsens and U.N.-sponsored peace talks make little progress, Russia is standing firm in its longtime support of Syrian President Bashar Assad — who has used chemical weapons against his own people on multiple occasions — and in opposition to any resolutions condemning his regime.

"Our Western partners in the Security Council ... proposed that we cooperate in working out a resolution. The ideas they shared with us were absolutely one-sided and detached from reality," Russian Foreign Minister Sergey Lavrov told the Interfax news agency.

He said the humanitarian resolution amounts to little more than "one-sided accusations aimed at the regime."

Limited options

Foreign policy observers say that while an international coalition negotiated a last-minute deal last summer with the Assad regime to destroy its chemical weapons stockpiles, there simply aren't many cards left to play if Russia continues to stand in the way of a full resolution of the crisis.

"I think Russia is going to do what Russia is going to do. Russia has its own interests. It is looking to accomplish the goals Russia feels are within its own geopolitical sphere. ... It's hard to say France would necessarily have any more leverage" than the U.S., said Robert Kron, a senior analyst at the Center for European Policy Analysis who specializes in European defense and trans-Atlantic security.

Mr. Kron noted that France under Mr. Hollande often has appeared more willing than the U.S. to use military force against the Assad regime. Indeed, in the weeks leading up to last year's chemical weapons agreement that helped avert military strikes, it was Mr. Hollande's government that most vocally pushed for action in Syria.

Still, Mr. Hollande and Mr. Obama favor a diplomatic end to the conflict rather than military intervention.

But such an outcome appears no closer than it did a few months ago.

"We are not making much progress," U.N.-Arab League Joint Special Representative Lakhdar Brahimi said Tuesday from Geneva, where peace talks between the Assad government and rebel forces resumed Monday. "We all owe it to the Syrian people to move a little bit faster than we are doing."

The United Nations also reported that at least 500,000 Syrians are unable to access food, clean water and other aid supplies because of security concerns. Snipers believed to be part of Mr. Assad's forces have fired on humanitarian convoys in parts of the country.

In addition to Syria, Mr. Obama and Mr. Hollande also attempted to present a unified front on Iran, where the U.S., France and other international partners have secured an agreement under which Iran will roll back parts of its nuclear program in exchange for a gradual easing of international sanctions.

There was a hint of pre-meeting tension when Mr. Kerry and other U.S. officials criticized as "not helpful" a major French trade delegation that descended on Tehran this month in anticipation of deals if and when the sanctions are removed. Israel and other critics of the outreach to Iran have warned that business considerations could trump security concerns in dealing with Iran's nuclear programs.

Mr. Obama gave a stark warning to Western businesses that prematurely try to cut deals with Iran.

"I can tell you that they do so at their own peril right now because we will come down on them like a ton of bricks with respect to the sanctions that we control," he said.

Mr. Hollande countered that he did not control the actions of private French trade delegations.

"The president of the republic is not the president of the employers union in France, and he certainly doesn't wish to be," he said. "Companies make their decisions when it comes to traveling, but I certainly let them know that sanctions were in force and would remain in force."