The Russian and U.S. air forces held a joint training exercise in Syria on Tuesday, Russian news agencies reported, citing a general with Russia's armed forces, while the U.S. downplayed the report, saying event was merely a test of safety protocols.

Russian and U.S. air forces held a joint training exercise in Syria on Tuesday meant to prevent dangerous encounters between their aircraft, Russia's defense ministry said.

Syria's skies have become increasingly crowded since Russia on Sept. 30 joined the Syrian air force in bombing insurgent targets, while a U.S.-led coalition pursues a separate air strike campaign in the country's civil war.

"There was a joint exercise with air crews and ground troops from the Russian and U.S. air forces," General Andrei Kartapolov said in a statement.

He said the exercise entailed Russian and coalition jets practicing close encounters in a special zone at a minimum distance of three aeronautical miles. Crews practiced communicating in English and Russian, he added.

Kartapolov also said Russia and Israel, Syria's neighbor to the southwest, were informing each other continually on the situation in Syrian air space.

But the Pentagon downplayed the Russian report, saying the interaction between one U.S. fighter aircraft and one Russian fighter aircraft in the skies over Syria was a 3-minute-long test tied to newly agreed safety protocols and not a military exercise.

Interfax news agency also reported, citing General Andrei Kartapolov, that Russia and Israel were informing each other continually on the situation in Syrian airspace.

Meanwhile, in an apparent effort to set the stage for transition talks, a Russian foreign ministry spokeswoman said that Moscow does not consider it a matter of principle that Syrian President Bashar Assad should stay in power.

Asked whether it was crucial for Moscow that Assad stays, Maria Zakharova said on the Ekho Moskvy radio station: "Absolutely not, we've never said that."

"What we did say is a regime change in Syria could become a local or even regional catastrophe," she said, adding that "only the Syrian people can decide the president's fate."

Russia is believed to be Assad's strongest backer and has previously balked at the West's suggestions that the Syrian president should be ousted.

Russia in September began carrying out air strikes at Islamic State fighters in Syria at Assad's request. Earlier on Tuesday, the Russian defense ministry stated that Russia's air force has flown 1,631 sorties and struck 2,084 militant targets since the start of its air strikes campaign.

Also on Tuesday, Deputy Foreign Minister Mikhail Bogdanov told Russian news agencies that Moscow is aiming to host a round of talks between Syrian officials and opposition leaders next week.

Bogdanov said the Syrian government has agreed to participate, but that it is unclear which opposition groups might come. He did not give a specific date for the proposed talks.

The talks are expected to be discussed Wednesday at a meeting between Russian Foreign Minister Sergey Lavrov and UN Syrian envoy Staffan de Mistura, Bogdanov said.

Assad made a surprise visit to Moscow last month, which was viewed as a signal that Russia ultimately seeks a political settlement after weeks of heavy airstrikes in Syria, although the terms of such an arrangement are uncertain.