PARIS -- Syria's government and the opposition have agreed to consider opening humanitarian access in the run-up to a peace conference that would bring the sides together for the first time, the top diplomats for Russia and the U.S. said Monday.

Speaking in the midst of a two-day series of meetings in Paris, Russian Foreign Minister Sergey Lavrov and U.S. Secretary of State John Kerry also said they were pressing for a cease-fire and prisoner exchange between the warring sides.

But Syria's government derided the meetings in Paris, saying in a statement they were "closer to illusions than reality and taken by people who are detached from reality and extremely far from any acceptable political logic." Russia has been one of Syria's closest allies.

And Lavrov questioned whether the Western-backed opposition -- which has not yet agreed to attend peace talks and has limited influence inside Syria -- was willing or able to carry out agreements in the face of intense infighting that has pitted al Qaeda-linked militants against more moderate factions. Nearly 700 rebel fighters have died in recent days.

"There are many terrorists in in Syria and they are becoming more numerous," Lavrov said. "When we talk about the need for a cease-fire, to unblock as many settlements as possible to provide humanitarian access, all those factors are taken into account. ... We do not want a cease-fire which would be used by terrorist groups. Because that would be against the interests of everyone."

The opposition Syrian National Coalition, nearing collapse, is in disarray ahead of the Jan. 22 talks and the Paris meetings were intended to pressure it to attend. But Kerry said the opposition had nonetheless agreed to consider a cease-fire, prisoner exchange and to facilitate humanitarian access to the thousands of people trapped behind battle lines.

Kerry acknowledged that "terrorists greatly complicated this equation," but warned that "If disorder is allowed to continue to grow, it is extremists who will benefit, and all the people who want peace and stability who will lose."

And while Kerry and Lavrov agreed on several points, their nations remained at an impasse on whether Iran, Syria's strongest ally, should attend the peace talks.

The Syrian National Coalition has struggled for credibility within Syria, as one rebel brigade after another has broken away and accused the exiled group of being out of touch.

The coalition is nearing collapse, with members split on whether to attend talks that would bring the opposition to the negotiating table with Syrian President Bashar Assad's representatives for the first time.

Kerry said he would welcome Iran's participation in the upcoming talks -- but only if Tehran signs off on earlier diplomatic agreements that any transitional government in Syria would not include Assad or his close allies.

The UN did not invite Iran to the Jan. 22 peace conference and the U.S. has long maintained that it cannot participate if it does not agree with its guiding principles.

Lavrov, however, said Iran should attend, adding that some participants have rejected parts of the earlier agreement. He did not specify, but Assad's government, which is sending a delegation, has said the president will not surrender power and may run again in elections due later this year.