GENEVA (Reuters) - The U.N. mediator for Syria said on Thursday he would hold talks with Russian Deputy Foreign Minister Gennady Gatilov in Geneva on Monday, and that the United States had declined to take part in any trilateral meeting for now.

Special Envoy to Syria Staffan de Mistura delivers remarks at a Security Council meeting on the situation in Syria at the United Nations Headquarters in New York, U.S., April 12, 2017. REUTERS/Stephanie Keith

They will evaluate discussions in the Kazakh capital Astana, planned for May 3-4, that are aimed at reviving the tattered ceasefire, and prospects for convening talks in Geneva between Syria’s warring sides later in May, de Mistura said.

“The trilateral meeting - as you know that was a possibility - is being postponed, it is not taking place on Monday. It will be a bilateral ... But the trilateral is not off the table, it is just being postponed,” he told reporters.

De Mistura, asked about the U.S. administration’s intent to participate, replied: “There is a clearly an intention to maintain and resume these trilateral meetings, and the date and circumstances were not conducive for this to happen on Monday.”

The United States carried out a missile strike on a Syrian air base this month after a chemical weapons attack that killed scores of people near Idlib on April 4. Both incidents have raised tensions between Washington and Moscow, the Syrian government’s ally.

“The U.S. welcomes discussions with Russia regarding the UN-led political process on Syria in Geneva, and we have met in the past in the trilateral U.S.-Russia-UN format. But at this time there is no new trilateral meeting scheduled,” a U.S. spokesman in Geneva said in an email.

De Mistura said that his team had just taken part in technical talks in Tehran, in preparation for the Astana talks organised by Russia, Iran and Turkey.

There had been “some type of movement regarding the issue of detainees ...and on possible issues related to demining as well,” he said, adding that he was seeking details.

De Mistura said the suicide bomb attack on Saturday on a convoy of evacuees from the rebel-besieged villages of Foua and Kefraya had killed more than 130 people, including 67 children, and wounded some 200. Evacuations resumed on Wednesday.

His humanitarian adviser Jan Egeland criticized the evacuation, part of a four-town exchange negotiated by Iran and Tahrir al-Sham, a jihadist alliance, with the involvement of Hezbollah. The United Nations had no role in the reciprocal exchange that also included fighters and civilians in two government-besieged towns, Madaya and Zabadani.

“This cannot be considered voluntary evacuations, these are people evacuated after years of besiegement,” Egeland said. “Is it voluntary if people in the end have only (one) option - starve and be bombed or go on a bus to an uncertain future?”