GENEVA - U.S., Russian and U.N. trilateral talks on Syria scheduled for Monday have been postponed, says U.N. Special Envoy for Syria Staffan de Mistura.

De Mistura says he does not know why the United States has decided against attending the meeting early next week, but believes Washington remains committed to the three-way discussions on the Syrian situation.

"I would say that the indication I got from Washington is exactly that, that there is clearly an intention to maintain and resume these trilateral meetings," he said. "And, the date and the circumstances were not conducive for this to happen on Monday, but that is certainly their intention."

In the meantime, de Mistura says he will be holding what he calls a very intense bilateral meeting on Monday with Russian Deputy Foreign Minister Gennady Gatilov. He says there are many things to discuss regarding the upcoming meeting in the Kazakh capital, Astana, and on the Geneva peace talks.

"Regarding Astana, it is still on as forecast," he said. "We will be involved again on a senior technical level in order to support what, at the moment, does not seem to be working, which is a cessation of hostilities."

Russia, Turkey and Iran are sponsors of the Astana negotiations on May 3 and 4, which will focus on arranging a cease-fire in Syria so peace talks in Geneva can proceed.

De Mistura says he will be watching developments on the ground to make sure the talks, set to resume sometime in May, have the best possible chance of success.