ISTANBUL — US President Joe Biden is reportedly preparing to formally recognize the 1915 mass killings of up to 1.5 million Armenians by the Ottoman Empire as genocide in a move that would further strain US-Turkey relations.

On April 24, Biden is expected to use the designation while marking Armenian Genocide Remembrance Day, becoming the first US president to do so since Ronald Reagan, who later retracted his statements following pressure from the Turkish government.

Ankara officials reject the term, maintaining far fewer Armenians lost their lives during what they claim was a broader World War I era conflict and that Ottoman officials did not commit systematic killings, in contrast to research by most historians who designate the events as genocide.

Nearly all US presidents have refrained from using the genocide term to maintain positive relations with NATO-allied Turkey, but despite a long list of grievances between Ankara and Washington, Biden may follow through on his campaign pledge for formal recognition, though some reports indicate he might make a last-minute reversal.