U.S. Secretary of State John Kerry said on Tuesday he hoped to announce in early August details of a U.S. plan for closer military cooperation and intelligence sharing with Russia on Syria.

Kerry, speaking after meeting with Russian Foreign Minister Sergei Lavrov on the sidelines of a meeting of Southeast Asian nations in Laos, said there had been progress in recent days on moving forward with the plan.

The proposal envisages Washington and Moscow sharing intelligence to coordinate air strikes against the al Qaeda-affiliated Nusra Front and prohibit the Syrian air force from attacking moderate rebel groups.

Kerry has defended the proposal despite deep skepticism among top American military and intelligence officials, including Secretary of Defense Ash Carter and chairman of the Joint Chiefs of Staff Joseph Dunford, over working with Russia.

"My hope is that somewhere in early August we would be in a position to stand up in front of you and tell you what we're able to do with the hopes it can make a difference to lives of people in Syria and to the course of the war," Kerry told a news conference in the capital Vientiane.

During the discussions, he and Lavrov outlined the next stage of implementing the plan, including a series of technical-level meetings to address concerns by the U.S. military and intelligence community.

"We are doing our homework, and a lot of that homework has been done in the last few days, and I will tell you has been done successfully," Kerry said.

Kerry's State Department and White House allies say the plan is the best chance to limit the fighting that is driving thousands of Syrian civilians, with some trained Islamic State group fighters mixed in, into exile in Europe, and preventing humanitarian aid from reaching tens of thousands more.

The meeting in Laos comes amid accusations that Russia is behind the hacking of Democratic National Committee (DNC) emails released by Wikileaks on Friday.

Kerry said he raised the issue of the emails with Lavrov during their meeting. Earlier, Lavrov brushed aside the accusations that Russia was involved, saying: "I don't want to use four-letter words."

Cyber security experts and U.S. officials have said there is evidence that Russia engineered the release of the emails in order to influence the U.S. presidential election.

The FBI said it was investigating a cyber intrusion at the DNC, which has led to discord as the party's convention in Philadelphia opens on Monday to nominate former U.S. secretary of state Hillary Clinton as its candidate.

Although the hacking of the DNC was known to officials and cyber security experts a month ago, the timing of the release of the contents of communications within the party is the concern for U.S. authorities.