ISTANBUL (Reuters) - Turkey returned its ambassador to the Vatican on Thursday, nearly 10 months after withdrawing him in protest against Pope Francis’ description of the century-old massacres of Christian Armenians as genocide.

Pope Francis holds a skullcap given to him by a faithful as he arrives to lead the weekly audience in Saint Peter's Square at the Vatican February 3, 2016. REUTERS/Max Rossi

The pope sparked a row with Turkey when he said the killing of up to 1.5 million Armenians in World War One was “the first genocide of the 20th century”, just days before commemorations to mark the centennial of the massacres in April.

Muslim Turkey promptly recalled its envoy. In diplomatic terms, a 10-month absence for an ambassador is a very long time.

Turkey accepts that many Christian Armenians were killed in clashes with Ottoman soldiers when Armenians lived in the empire ruled from Istanbul, but denies hundreds of thousands were killed and that this amounted to genocide.

Tanju Bilgic, the Turkish Foreign Ministry’s spokesman, said the decision came after the Vatican on Wednesday praised Turkey’s willingness to open its archives to historians and create a joint commission of scholars to explore past events.

The Vatican comment was within a statement about the pope having received a book by an Italian author about a naval battle between Turkey and the Venetian Republic in 1657.

Francis is given many books at his general audiences on Wednesdays but the Vatican rarely issues statements about them, so praise for Turkey in the context of the book was a sign that the Holy See way trying to find a solution to the impasse, a diplomatic source said.

In the statement the Vatican also recognised the killing of a Turkish ambassador to the Holy See in 1977 by Armenian gunmen as terrorism, which Turkey “appreciated”, Bilgic said.

Turkey routinely withdraws its representatives in countries that decide to recognise the killing of Armenians as genocide.

An overwhelming majority of Turks reject the accusation of genocide. The issue continues to thwart efforts to re-open diplomatic ties with neighbouring Armenia, and their 300-km (190-mile) border has been closed for two decades.

(This version of the story corrects paragraph 4 to say Armenians lived in Ottoman empire, not Armenia was part of it)