US Defence Secretary Ash Carter called on Moscow today to urgently respond to proposed rules for air-to-air conduct over Syria, as he condemned Russia's "seriously irresponsible and unprofessional" violation of Turkish air space.
The United States and Russian militaries held a secure video conference last week in which Pentagon officials suggested protocols aimed at preventing a mishap, as the former Cold War foes carry out rival campaigns of air strikes in Syria.
But since then, Moscow has failed to follow-up, Carter said.
"We are waiting for the Russians. They owe us a response," Carter told reporters as he visited Moron Air Base in Spain.
"They should come in and do it right now."
The discussions on ways to keep the U.S. and Russian aircraft from clashing have gained urgency after the United States and NATO denounced Russia for violating Turkish airspace. Turkey, a NATO ally, threatened to respond, raising the prospect of direct confrontation.
Russian Deputy Defence Minister Anatoly Antonov said Moscow would welcome a Turkish Defence Ministry delegation to discuss avoiding any "misunderstandings" in Syria.
The U.S. proposal includes basic safety protocols, such as maintaining a safe distance between U.S. and Russian aircraft and using common radio frequencies for distress calls, officials say, adding they would be similar to civil aviation.
Carter expressed frustration that Russia, after calling for talks with the United States, had let so much time elapse before getting back in touch on the U.S. proposals for air conduct.
"It's only professional that you follow through on the requests they made and they've not done that yet. And that may be a further sign of their strategic confusion, I don't know," he said.
The United States and Russia say they have the same enemies - the Islamic State group of Sunni Muslim militants who have proclaimed a caliphate across eastern Syria and northern Iraq.
But United States fiercely opposes Moscow's support for Syrian President Bashar al-Assad and accuses Moscow of mainly targeting other insurgents who oppose Assad, rather than Islamic State.
Carter said Moscow's strategy of bolstering Assad would backfire.
"In Syria, they are going to be checked in the first instance by the backlash that they're going to get on account of siding with Assad against everyone else," Carter said.