Turkey could shut down its Incirlik airbase, which hosts US nuclear warheads, in response to possible US sanctions and a separate Senate resolution that recognized mass killings of Armenians as genocide, President Recep Tayyip Erdogan said on Sunday. "If it is necessary for us to take such a step, of course we have the authority ... If this is necessary, together with our delegations, we will close down Incirlik if necessary," Erdogan said on A Haber TV. Turkey can also close down the Kurecik radar base if necessary, he said. "If they are threatening us with the implementation of these sanctions, of course we will be retaliating," he added. Incirlik airbase in southern Turkey has been a main base for US operations in the Middle East and more recently in the fight against ISIS in Syria and Iraq, while Kurecik, in eastern Turkey, is a key NATO base. Turkeys decision to proceed with the purchase of the Russian-made S-400 missile defense systems has added to growing tensions between the two NATO allies. Washington says the Russian system poses a threat to NATO and has removed Turkey from the US-led F-35 stealth fighter jet program. As for the US Senate measure last week, it was condemned by Turkey. US Ambassador David Satterfield was summoned to the Turkish Foreign Ministry, where Deputy Foreign Minister Sedat Oney conveyed Turkeys "strong reaction" to the Senate action, a ministry official said Friday. Historians estimate that up to 1.5 million Armenians were killed around World War I, a mass loss of life that many scholars regard as the 20th centurys first genocide. Turkey disputes the description, saying the death toll was inflated and those killed were victims of a civil war. Erdogan suggested on Sunday that Turkey could also respond with parliamentary resolutions recognizing the killings of indigenous Americans in past centuries as genocide.