WASHINGTON 

The pilots of a downed Russian aircraft did not respond to Turkish military warnings, a spokesman for the U.S.-led anti-Daesh coalition said Tuesday.

Col. Steve Warren said coalition headquarters heard the incident on radar and confirmed Turkey’s military claim regarding the lack of response from the Russian pilots. The pilots were warned 10 times in 5 minutes, according to the Turkish Armed Forces. 

Warren described the downing of the aircraft as "an incident between the Russian and the Turkish governments” and not one involving the coalition.

International norms prohibits an alien aircraft from flying over another state's airspace, he said. 

"International norms are clear and well known by all players so there is no reason for an aircraft to fly over an area it shouldn't," Warren said. 

Two Turkish F-16s on patrol along the Syrian border engaged two Russian SU-24s before shooting one down after the warnings. 

The Russian defense ministry has announced an investigation into the crash.

Russian authorities said their planes were after Daesh in the area when it crossed the border.

Warren, however, said there are no Daesh targets in that area, expressing concern about Russian activities in Syria that go beyond targeting Daesh. 

Russian aircraft have accompanied forces of Syrian President Bashar al-Assad that are conducting offensives against opposition groups. 

Russian jets twice violated Turkish airspace last month. 

The U.S. last month deployed six F-15C air-to-air fighter jets to the Incirlik Air Base in southern Turkey to help Turkish jets patrol its borders. 

Warren told reporters that none of those U.S. aircraft were involved in the incident and there were no American aircraft or equipment in the vicinity where the incident happened. 

He noted, however, the F-15s that are protecting Turkish airspace are not part of the coalition and not operating within the parameters of an agreement singed last month with Russia about air safety above Syria. 

Warren declined to get into the rules of engagement of those aircraft.

Pentagon spokesman Peter Cook described the Turkish airspace as "NATO airspace" reiterating the U.S. support to the NATO ally's actions to defend the alliance's southern flank. 

Noting Pentagon's efforts to collect the details about the incident Cook added: "There were previous incursions that, of course, made the Turks concerned and as a NATO ally, we had concerns as well... Turkey has a right to defend its airspace."

The spokesman also dismissed the comparisons between Turkish fighters’ action and U.S. fighters escorting Russian bombers out of the American airspace when they approach the coasts of the U.S. 

"This is obviously a conflict zone right now, given the fight over Syria," he said. "This is a particular circumstance with particular aspects to it."

He also warned against a risk for miscalculation over the incident.