Arguments have raged for decades about the Armenian deaths

The decision has delighted Armenians and infuriated Turks.

Why put "genocide" in inverted commas?

Whether or not the deaths of hundreds of thousands of Armenians during World War I amounted to genocide is a matter for heated debate. Many Western historians believe it falls into the category of genocide. Some countries have declared that a genocide took place, but others have resisted calls to do so.

What happened?

During World War I, as the Ottoman Turkish empire fought Russian forces, some of the Armenian minority in eastern Anatolia sided with the Russians.

Turkey took reprisals. On 24 April 1915 it rounded up and killed hundreds of Armenian community leaders.

In May 1915, the Armenian minority, two or three million strong, was forcefully deported and marched from the Anatolian borders towards Syria and Mesopotamia (now Iraq). Many died en route.

What do Armenians say?

Armenians say 1.5 million of their people were killed in this period, either through systematic massacres or through starvation.

They allege that a deliberate genocide was carried out by the Ottoman Turkish empire.

What does Turkey say?

It says there was no genocide.

It acknowledges that many Armenians died, but says Turks died too, and that massacres were committed on both sides as a result of inter-ethnic violence and the wider world war.

What is genocide?

Article Two of the UN Convention on Genocide of December 1948 describes genocide as carrying out acts intended "to destroy, in whole or in part, a national, ethnic, racial or religious group".

What do others say?

France, Russia, Canada and Uruguay are among those countries which have formally recognised genocide against the Armenians.

The UK, US and Israel are among those that use different terminology.

Why does the row continue?

Armenians are one of the world's most dispersed peoples. While in Armenia, Genocide Memorial Day is commemorated across the country, it is the diaspora that has lobbied for recognition from the outside world. The killings are regarded as the seminal event of modern Armenian history, and one that binds the diaspora together.

In Turkey, the penal code makes calling "for the recognition of the Armenian genocide" illegal. Writers and translators have been prosecuted for attempting to stimulate debate on the subject.

Turkey has condemned countries that recognise the Armenian genocide, and was furious when the French parliament passed a bill outlawing denial of it.