“We agreed that we are both serious, more than serious, committed,” Mr. Kerry said after meeting here in the Brunei capital with his Russian counterpart, Foreign Minister Sergey V. Lavrov.
But Mr. Kerry indicated that there were still differences with the Kremlin over the conference and suggested that it might not be held before September because of the press of other diplomatic business and the practice of European and other leaders to go on vacation in August.
Mr. Kerry made his remarks in a statement at the American Embassy here, and he did not take any questions.
In his meeting with Mr. Lavrov, Mr. Kerry also reiterated the Obama administration’s request that Edward J. Snowden, the former security contractor who has fled to Moscow, be returned to the United States. But Mr. Kerry said Mr. Snowden’s fate was not part of Mr. Lavrov’s “portfolio.”
The two diplomats met on the margins of a conference that was hosted by Southeast Asian nations.
Mr. Kerry first sought the Kremlin’s backing for the Syrian peace conference, to be held in Geneva, during a May trip to Moscow. At that time, Mr. Kerry indicated that the gathering, which would bring together the Syrian opposition with representatives of the government of President Bashar al-Assad, might take place by the end of May.
But the push for the peace conference was almost immediately overtaken by events as the Assad government, drawing on arms supplied by Iran and fighters from Hezbollah, the militant Lebanese group, made gains on the battlefield.
A weakened Syrian opposition faced the prospect of attending a conference to negotiate with representatives of a reinvigorated Assad government. Gen. Salim Idris, the senior rebel commander, said in early June that the opposition would not attend unless additional arms were sent to the rebels.
Since then, President Obama decided to covertly supply light arms, ammunition and possibly antitank weapons to the Syrian opposition, an administration official said last month.
Still, questions remain whether the steps taken by the United States and its partners are sufficient to tilt the military balance in Syria and whether the conference can achieve its main goal of fostering a political transition to a post-Assad government if Mr. Assad still believes he can prevail.
In recent months, Mr. Kerry has repeatedly stressed that it is vital to take steps to change the “calculation” of Mr. Assad that he can hold onto power so that a political settlement may be worked out. But on Tuesday, Mr. Kerry argued instead that military developments were not so important.
“Whether the regime is doing better or the opposition is doing better is frankly not determinative of that outcome because the outcome requires a transition government,” he said, referring to efforts to negotiate a political settlement.
Virtually since plans for the Geneva conference were announced in May, the United States and Russia have had differences over its purpose and structure.
During their initial discussions about organizing the meeting, the Russians argued that Iran, a staunch backer of the Assad government, be included.
The United States was opposed to including Iran, proposing instead that it include the “London 11,” a coalition of Western and Arab nations that has been supporting the Syrian opposition.
The Russians also suggested that multiple delegations from the Syrian opposition attend. Fearing that that would dilute the opposition’s influence, the United States has insisted that a unified Syrian opposition delegation attend.
A more fundamental point of contention has been the United States’ insistence that Mr. Assad cannot be part of the political solution. The Russians have not only supported Mr. Assad politically but have been also providing weapons to the Syrian government.
In his comments on Tuesday, Mr. Kerry said the two sides had “narrowed down some of the options with respect to the potential of that conference.” But he provided no details on what matters were now agreed upon and what differences remained.
Mr. Lavrov, for his part, asserted that one problem was disarray among the Syrian opposition and the demand of some of its members that Mr. Assad’s departure be a precondition for talks.
“Our American partners recognize that the main thing is to secure the consolidation of the Syrian opposition,” Mr. Lavrov told Russian journalists, according to the Russian news agency Interfax.
Mr. Kerry did not say when a Syria peace conference might take place. He said the next several weeks were a problem because he and Defense Secretary Chuck Hagel had to attend a meeting with their Russian counterparts in Washington in August. Another factor, he added, is the vacation patterns of European leaders.
“Obviously August is very difficult for Europeans and others, so it may be somewhat thereafter,” he said.