Secretary of State John Kerry on Friday said that talks with Russia on disarming Syria’s chemical weapons had been “constructive” but cautioned that there was more work to do ahead of broader peace talks aimed at ending that country’s two-year civil war.

Kerry and Russian counterpart Sergey Lavrov met with United Nations-Arab League envoy Lakhdar Brahimi on Friday in Geneva. Brahimi is organizing a broader summit scheduled for late September in New York to coincide with the UN General Assembly meeting to help bring a peaceful end to the Syrian civil war.

“We are working hard to find the common ground to be able to make that happen and we discussed some of the homework that we both need to do,” said Kerry at a joint press conference.

“I'm not going to go into it in any detail today,” said Kerry, who remained tight-lipped about the status of negotiations, but stressed that both sides were committed to forging a deal on placing Syria’s chemical arsenal under international control to avert a threatened U.S. military strike.

President Obama is threatening to use military force to punish Syrian leader Bashar Assad's alleged use of chemical weapons against civilians in an attack on Aug. 21. But the president’s call has faced strong opposition in Congress and from the American public.

In a national address Tuesday, Obama said he would pursue a Russian offer to persuade Syria to turn over its chemical weapons arsenal to international control.

“President Obama is deeply committed to a negotiated solution with respect to Syria, and we know that Russia is likewise,” Kerry told reporters.

But Kerry cautioned that the success of any deal would hinge on Syria compliance.

Lavrov said the talks had been “useful” and touted the Assad regime's new commitment to join the Chemical Weapons Convention, the international treaty banning chemical arms. The Russian minister called it a major step in trying to resolve the dispute over Syria’s weapons of mass destruction “quickly, professionally” and “as soon as practical.”

The timetable for Syria to disclose the locations of its chemical weapons and place them under international control has quickly become a sticking point in the nascent negotiations.

Kerry and top White House officials have said they are not interested in delaying tactics and remain skeptical that Assad will cooperate quickly to put his full arsenal under international control and make arrangements to have it destroyed.

Assad on Thursday continued to deny any involvement in the Aug. 21 chemical attack, but announced that his country had formally applied to join the chemical weapons treaty.

The treaty requires countries to declare the types, quantities and locations of all chemical weapons as well as the location of production and storage facilities within 60 days of joining the accord.

Kerry has said normal procedures are far too slow and shouldn't apply to Syria because they had used those weapons recently.

“There is nothing standard about this process because of the way the regime has behaved,” Kerry said Thursday. “The words of the Syrian regime in our judgment are simply not enough.”

Kerry also credited Obama for Assad’s decision to sign the chemical weapons treaty and disarm. The secretary of State said that only Obama’s threat of military action had convinced Assad to change his stance. He also vowed that the U.S. would keep the threat of a strike on the table to ensure Assad surrendered control of his stockpile.

The tensions between the U.S. and Russia are still evident at the talks.

Appearing put off by the length of Kerry's opening statement at a press conference on Thursday, Lavrov said he wasn't prepared to offer an “extended political statement.”

“Diplomacy likes silence,” he said.

The White House has also declined to provide a timetable for talks, despite concerns from many lawmakers that the negotiations are a stalling tactic by Russia and could allow Assad to solidify his hold on Syria.

The Wall Street Journal on Friday reported that a secretive Syrian military unit has been moving stocks of poison gases and munitions to as many as 50 sites to make it harder for the U.S. to track.

U.S. and Israeli intelligence agencies still believe they know where most of the Syrian regime's chemical weapons are located, but with less confidence than six months ago, according to the report.