YEREVAN, Armenia (AP) — About 10,000 people bearing torches on Sunday night marched through Armenia’s capital to commemorate the estimated 1.5 million Armenians killed in Ottoman Turkey more than a century ago.

The march from a central square to a sprawling memorial complex began with activists burning the flags of Turkey and Azerbaijan. Tensions between Armenia and Azerbaijan have spiraled in recent months since the blockage of the road leading to the ethnic Aremenian region of Nagorno-Karabakh within Azerbaijan.

Historians estimate that, in the last days of the Ottoman Empire, up to 1.5 million Armenians were killed by Ottoman Turks in what is widely regarded as the first genocide of the 20th century.

Armenians have long pushed for the deaths to be recognized as genocide.

While Turkey concedes that many died in that era, the country has rejected the term genocide, saying the death toll is inflated and the deaths resulted from civil unrest during the Ottoman Empire’s collapse.

Armenia on Monday formally observes Genocide Remembrance Day, marking the start of the killings in 1915.