Turkish President Recep Tayyip Erdogan is challenging nations who label the mass killings of Armenians by Ottoman Turks as genocide, saying they should inspect Turkey's Ottoman-era archives and "we have nothing to hide."

Marking April 24, 1915, considered the start of the massacre of the Armenians, Erdogan said nations who accuse Turkey of genocide have a "bloody past."

Historians estimate up to 1.5 million Armenians were killed around World War I, and many scholars see it as the 20th century's first genocide. Turkey disputes the description, says the toll has been inflated and considers those killed victims of a civil war.

Erdogan said: "when you dig into massacres, genocides (and) torture ., you will find those who cry 'genocide, democracy, freedom' against us."