Turkey opposes that definition, and many countries, including the USA, haven't labeled the massacre as a genocide.
Turkey, the successor to the Ottoman Empire, vehemently denies that the massacre was genocide and insists it was part of the violence during World War I.
The statement was criticized by the Armenian National Committee of America (ANCA) and the Armenian Assembly of America (AAA), which accused Trump of "caving in to Turkish pressure".
The U.S. first recognized the Armenian Genocide in 1951 through a filing which was included in the International Court of Justice (ICJ) Report titled: "Reservations to the Convention on the Prevention and Punishment of the Crime of Genocide".
In a message sent to the Armenian Patriarchate of Constantinople, Erdogan offered condolences to the grandchildren of the Ottoman Armenians "who lost their lives during the war".
Armenians worldwide hold annual commemorations on April 24 marking the mass killings, which remain a diplomatic minefield amid a lack of global consensus over Armenia's bid to get the deaths recognized internationally as a genocide.More news: Trump Lawyers Arrive At NY Federal Court
Armenia claims 1.5 million died under the Ottoman empire in 1915.
The former United States presidents, starting from 1981, including Barack Obama, also refused to call the historical events a "genocide".
The Armenian Genocide perpetrated by the Ottoman government has been documented, recognized and acknowledged by eyewitness reports, laws, resolutions and the decisions of numerous states and worldwide organizations.
"We reject the inaccurate expressions and the subjective interpretation of history in the written statement by Mr. Donald Trump, President of the U.S., released on 24 April 2018 regarding the events of 1915", the statement said.
Trump also said he stood "with the Armenian people throughout the world in honoring the memory of those lost", reiterating his commitment to working with the community to build a better and more tolerant future.