Coming shifts in the U.S. military's footprint in Europe will include sending warplanes and support troops into Turkey to help fight Islamic State militants and moving more heavy Army equipment into Eastern Europe to deter Russian aggression, the top U.S. commander in the region said Friday.

"Europe isn't what it was 18 months ago, or even six months ago. And new threats and challenges seemingly emerge every day," Air Force Gen. Philip Breedlove, chief of U.S. European Command, told reporters at the Pentagon.

The U.S. will be sending a detachment of F-15 aircraft to Incirlik Air Base in Turkey to join the current fleet of 12 A-10s, a senior administration official told Military Times.

Incirlik Air Base in southern Turkey is close to many Islamic State strongholds, and moving more assets there would cut response times for U.S. aircraft and increase the efficiency of operations against the group.

The aircraft also will provide "support to our Turkish ally as we help them to address their concerns about their airspace," Breedlove said. Turkey, a NATO ally, recently has complained about Russian aircraft violating its airspace.

Moving F-15s into Turkey will expand the existing fighter fleet that arrived for the first time earlier this year. A breakthrough deal with the Turkish government this summer allowed the U.S. to deploy combat aircraft to Incirlik; U.S. access to that base previously was limited to cargo and intelligence, surveillance and reconnaissance aircraft.

It is unclear how many additional U.S. troops will be moving to Incirlik; about 1,900 are there now.

After drawing down force levels in Europe for two decades since the end of the Cold War, the U.S. and its NATO allies are becoming increasingly concerned with Moscow's aggressive and unpredictable behavior and the formidable military capability that Russian leaders have aligned along their European border.

"Our force structure in Europe now is not adequate" to the task of deterring the larger Russian presence along the continent's eastern frontier, the general said.

The number of U.S. troops deployed to EUCOM is unlikely to change, Breedlove said. But temporary rotations of units from outside the command may help boost warfighting capability along NATO's eastern flank, including Poland, Romania, Bulgaria and the Baltic states.

The Pentagon plans to send more gear to "pre-position" in Eastern Europe in addition to the heavy brigade's worth of equipment that has been moving into the region this year. That includes armored vehicles, artillery, ammunition stocks and communications equipment.

"We're now looking at what further pre-position materiel we need to address," Breedlove said. "The ability to rapidly reinforce Europe will rely first on fast-moving troops falling in on pre-positioned material. And so, we need to have the appropriate composition and type of pre-positioned materiels put forward.

"We'll roll that out over the next months."

U.S. forces in Europe and NATO partners are conducting the largest military exercise in more than a decade. "Trident Juncture," involving more than 36,000 troops, aims to "test the NATO response force, a high-readiness and technologically advanced force comprised of land, air, maritime and special force units, capable of being deployed quickly to support our operations wherever needed," Breedlove said.

Breedlove acknowledged that Western leaders still have not fully discerned Russian President Vladimir Putin's intent with his recent military actions.

"But I can observe the capabilities and capacities that Russia is creating across our [area of responsibility]," he said. "And I continue to believe that we must strengthen our deterrence and that EUCOM and our NATO allies must continue to adapt by improving our readiness and responsiveness."