Russia and the United States are set to renew talks to avoid accidents in Syrian air space as the two countries conduct separate bombing campaigns, a US official said Friday.

The Pentagon expressed alarm this week after Russia failed to quickly answer proposals made during initial talks, even as it launched cruise missiles from the Caspian Sea and repeatedly violated Turkish air space.

But on Friday, Pentagon press secretary Peter Cook said Moscow had filed an appropriate response.

"The Department of Defense has received a formal response from the Russian ministry of defense regarding DoD's proposal to ensure safe air operations over Syria," Cook said.

"Department leaders are reviewing the Russian response and talks are likely to take place as soon as this weekend."

US officials were furious after Russia only gave them a vague, verbal "heads-up" about an hour before Moscow launched its bombing campaign on September 30.

The two countries had "deconfliction" talks the next day via videoconference, aimed at ensuring Russian warplanes didn't cross paths with drones and US-led coalition jets.

Talks center around basic safety measures including which language air crews should communicate in and how much space planes should leave each other.

Russian planes have flown near a US drone, officials say, and the US military has had to reroute some flights to avoid any close calls.

The Pentagon for weeks watched Russia build up its military presence in northwestern Syria, but the launch of Moscow's campaign seemed to catch officials off guard.

The United States has since last year led a 60-plus member coalition of nations bombing Islamic State jihadists in Iraq and Syria.

Also Friday, the Obama administration announced plans to overhaul the Pentagon's much-criticized program to train and equip moderate Syrian rebels to fight IS in Syria.

Instead of training units of troops to fight, the program is being "refocused" to arm selected rebel leaders whose groups have been battling IS in Syria.

These groups, boosted by US-supplied weapons, will supposedly push into IS territory in Syria.