The Kremlin said on Friday there was no time frame for its military operation in Syria.
Russia's Izvestia newspaper reported that a group of Su-24 and Su-34 warplanes had arrived at Syria's Hmeymim base, Reuters reported.

The Su-25 is an armored twin-engine jet that was battle-tested in the 1980s during the Soviet war in Afghanistan. It can be used to strafe targets on the ground, or as a bomber.

Russia's defense ministry did not immediately respond to a request from Reuters for comment. The US State and Defense Departments declined comment on the Izvestia report.

Earlier, US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov spoke by telephone for a third straight day, with the top Russian diplomat saying Moscow was ready to consider more ways to normalize the situation in Aleppo.

But Lavrov criticized Washington's failure to separate moderate rebel groups from terrorists, which had allowed forces led by the group formerly known as the Nusra front to violate the US-Russian truce agreed on September 9.

The United States made clear on Friday that it would not, at least for now, carry through on the threat it made on Wednesday to halt the diplomacy if Russia did not take immediate steps to halt the violence.

"This is on life support, but it's not flat-lined yet," State Department spokesman Mark Toner told reporters. "We have seen enough that we don't want to definitively close the door yet."

Syria has been gripped by civil war since March 2011 with various terrorist groups, including Daesh (also known as ISIS or ISIL), currently controlling parts of it.

According to a report by the Syrian Center for Policy Research, the conflict has claimed the lives of over 470,000 people, injured 1.9 million others, and displaced nearly half of the country’s pre-war population of about 23 million within or beyond its borders; Tasnim News reported.

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