By Dominic Evans and Orhan Coskun
ISTANBUL (Reuters) - U.S. President Joe Biden's declaration that the massacres of Armenians in the Ottoman Empire constituted genocide is "simply outrageous" and Turkey will respond in various ways over the coming months, Turkey's presidential spokesman said on Sunday.
Biden broke on Saturday with decades of carefully calibrated White House comments over the killings in 1915, delighting Armenia and its diaspora in the United States but further straining ties between Washington and Ankara, two NATO allies.
"There will be a reaction of different forms and kinds and degrees in coming days and months," Ibrahim Kalin, President Tayyip Erdogan's spokesman and adviser, told Reuters in an interview.
Kalin did not specify whether Ankara would restrict U.S. access to the Incirlik air base in southern Turkey, which has been used to support the international coalition fighting Islamic State in Syria and Iraq, or other measures it may take.
Turkish officials swiftly condemned Biden's statement on Saturday, and Kalin said Erdogan would address the issue after a cabinet meeting on Monday. "At a time and place that we consider to be appropriate, we will continue to respond to this very unfortunate unfair statement," he said.
Turkey accepts that many Armenians living in the Ottoman Empire were killed in clashes with Ottoman forces in World War One, but denies the killings were systematically orchestrated and constitute a genocide.
For decades, measures recognising the Armenian genocide stalled in the U.S. Congress and most U.S. presidents have refrained from calling it that, stymied by concerns about relations with Turkey and intense lobbying by Ankara.
But those relations are already troubled. Washington has put sanctions on Turkey over its purchase of Russian air defences, while Ankara has been angered that the United States has armed Kurdish YPG fighters in Syria and not extradited a U.S.-based cleric Turkey accuses of orchestrating a 2016 coup attempt.
Navigating those disputes will now be even harder, Kalin said. "Everything that we conduct with the United States will be under the spell of this very unfortunate statement," he said.
Kalin said U.S. officials had told Turkey that the declaration would not provide any legal basis for potential claims of reparations over the killings.
Nevertheless, Erdogan told the U.S. president when they spoke by phone on Friday, their first conversation since Biden took office three months ago, that it would be a "colossal mistake" to go ahead with his statement.
"To reduce all that to one word and try to implicate that Turks were involved, our Ottoman ancestors were involved in genocidal acts is simply outrageous," Kalin said. "It's not supported by historical fact".
(Reporting by Dominic Evans and Orhan Coskun; Editing by Ece Toksabay and)