The US and Russia are to hold new talks on air safety in Syria after it emerged combat aircraft from both nations came within miles of each other on Saturday.
The planes were in visual contact with each other, 10 to 20 miles (15-30km) apart, a US defence spokesman told reporters in Washington DC.
It will be the third round of talks as the two countries seek to find ways of avoiding an accidental conflict.
Despite the talks, the US said Russia's actions in Syria were "wrongheaded".
US Secretary of Defence Ash Carter said he expected a deal soon. Russia said it had "updated proposals" to be discussed during a video conference.
Russia began its campaign of air strikes in Syria on 30 September, saying it was targeting Islamic State (IS) militants and other jihadist groups after a request to help militarily from Syrian President Bashar al-Assad.
Western countries and Syrian activists say Russian planes have been hitting non-militant targets — a claim Moscow denies.
In a separate development on Tuesday, two shells struck the Russian embassy compound in the Syrian capital Damascus as hundreds of pro-government supporters rallied outside in support of Russian air strikes.
No-one was killed but a BBC Arabic correspondent in Damascus says some people were injured.
Russia described the shelling as "a terrorist attack".
'Same battle space'
US and Russian officials are expected to hold a video conference later on Wednesday.
Ahead of the talks, Mr Carter said: "Our talks… are very professional, they're very constructive, and I expect them to lead in very short order to an agreement."
But he stressed that the Americans "are not able at this time to associate ourselves more broadly with Russia's approach in Syria because it is wrongheaded and strategically short-sighted".
Meanwhile, the Russian defence ministry said it had "updated proposals on Syria for the US" and was waiting for a "third video conference".
The talks come after US military spokesman Col Steve Warren told reporters that two US and two Russian aircraft "entered the same battle space" over Syria on Saturday.
He said the aircraft were in visual contact with each other.
Col Warren also said that Russian planes had repeatedly broken air patrols, coming close to US American unmanned aerial vehicles or drone aircraft.
Russia has not publicly commented on this claim.