Russian Foreign Ministry spokesperson Maria Zakharova on Monday slammed the United States for its refusal to participate in the 10th round of international talks on Syria in Russia's Sochi.

Moscow invited Washington to the Syrian talks in the Astana format on Monday and Tuesday as an observer, but the U.S. side declined it, Zakharova said in a statement on the foreign ministry's website.

"This response is regrettable, keeping in mind that Washington constantly gives assurances that it is willing to help the political process take place in Syria," she said.

"We see the U.S. reluctance to send representatives to Sochi as a desire to lower the importance of the Astana format and discredit the implementation of the mediatory efforts in Syrian affairs that Washington is unable to put under its control," she added.

According to Zakharova, the Astana process is in no way an alternative to the UN-sponsored Geneva talks.

She said the U.S. call to prioritize the Geneva process "looks disingenuous" as UN secretary-general's special envoy for Syria Staffan de Mistura is taking part in the Sochi event.

In parallel to the Geneva process, nine rounds of Syrian talks had been held in the Kazakh capital of Astana since January 2017, with Russia, Turkey and Iran as the mediators.

The negotiations moved from Astana to Russia's Sochi for the first time. The most significant outcome of previous talks was the establishment of four de-escalation zones in Syria.