A day after vowing closer defense cooperation with Russia, Turkey said Wednesday it would seek "alternatives" to the F-35 fighter jet program the United States has excluded it from.

Washington said last month Turkey will be scrapped from the F-35 program after Ankara bought Russian S-400 air defense systems.

"We need war jets. If we cannot buy the F-35s, we will look for new alternatives," official news agency Anadolu quoted Foreign Minister Mevlut Cavusoglu as saying in the Estonian capital of Tallinn.

Turkey has lambasted as "unfair" the US move to exclude it from the F-35 Joint Strike Fighter program. The White House said the jet could not "coexist with a Russian intelligence collection platform that will be used to learn about its advanced capabilities."

Turkey has said it plans to start using the S-400 missile defense system by April 2020. The second phase of delivery began Tuesday.

Ankara had ordered more than 100 F-35 jets and its defense industry has invested significant sums in the plane's development.

On Tuesday, President Recep Tayyip Erdogan met his counterpart Vladimir Putin on the margins of the MAKS international air show, a showcase for Russia's military and civilian aerospace industry.

Putin said he and Erdogan had discussed further military cooperation, including on Russia's Sukhoi Su-35 fighter jet, while the Turkish leader expressed Ankara's willingness to continue defense collaboration.