Armenian President Serzh Sarkisian on Thursday accused Turkey of an "utter denial" in failing to recognise World War I mass killings of Armenians in the Ottoman Empire as genocide, apparently brushing off Ankara's first ever offer of condolences for the tragedy.

In an unprecedented move described by the United States as a historic gesture, Turkish Prime Minister Recep Tayyip Erdogan on Wednesday offered condolences over the massacres, calling them "our shared pain."

But in a statement marking the 99th anniversary of the start of the killings and mass deportations, Sarkisian made no acknowledgement of Erdogan's move and instead accused Turkey of continuing to ignore the facts.

"The Armenian genocide... is alive as far as the successor of the Ottoman Turkey continues its policy of utter denial," he said.

"The denial of a crime constitutes the direct continuation of that very crime," he added. "Only recognition and condemnation can prevent the repetition of such crimes in the future."

He said the looming 100th anniversary offered "Turkey a good chance to repent and to set aside the historical stigma in case if they make efforts to set free their state's future from this heavy burden."

He also stressed that the events of 1915 "should not prevent Turks and Armenians from establishing compassion and mutually humane attitudes towards one another."