Turkey has renovated a 1,100-year-old church in the east of the country, in what is seen as a gesture to improve ties with neighbouring Armenia.
The church had long been neglected
The ceremony on Akdamar island on Lake Van was attended by senior Armenian officials, despite the two countries' lack of diplomatic ties.
The mass killings of Armenians by Ottoman Turks in 1915 left profound scars and bitterness.
About 70,000 Armenians live in Turkey today. The church will now be a museum.
Plea for worship
Patriarch Mesrob II, spiritual leader of Turkey's tiny Armenian Orthodox community, told several hundred people at the ceremony that the government should open up the restored church for worship at least once a year.
The church has fine carvings of saints on its facade
He said the move would help reconciliation between Turks and Armenians.
"If our government approves, it will contribute to peace between two communities who have not been able to come together for years," he said.
Turkish Culture Minister Attila Koc said Ankara would consider the request.
But the head of Armenia's Apostolic Church, Garegin II, declined Ankara's invitation to attend the ceremony because the church will no longer function as a place of worship.
So far Turkey has ignored calls to place a cross on the conical roof.
The Church of Surp Khach - or Holy Cross - is one of the finest surviving monuments of Armenian culture in the region. Its location is called Akhtamar in Armenian.
It had long been left empty and neglected, its intricate wall carvings depicting biblical scenes crumbling.
The Turkish government spent $1.5m (£763,000) on its restoration, which took 18 months to complete.
The 20-strong Armenian delegation of architects, engineers and archaeologists attending the ceremony was headed by Deputy Culture Minister Gagik Gyurjyan.
Mr Gyurjyan said they were not in Turkey just to witness the renovation of the church, which was built between 915-921.
"We think we can discuss new projects regarding the future," he said, according to Turkey's Anatolia news agency.
"Our experts can co-operate in many areas including archaeology, architecture and industry."
But relations between the two countries remain tense.
Turkey closed its border with Armenia in the 1990s to support Azerbaijan in its dispute with Armenia over Nagorno-Karabakh. To get to Akdamar, Armenian officials had to travel via Istanbul or Georgia.
Armenians say 1.5 million of their people were killed in a genocide by Ottoman Turks during World War I, either through systematic massacres or through starvation.
More than a dozen countries, various international bodies and many Western historians agree that it was genocide.
Turkey says there was no genocide. It acknowledges that many Armenians died, but says the figure was below one million.
Police reportedly detained five trade unionists who staged a demonstration on a jetty on Lake Van to protest against the church's restoration.
The protesters carried Turkish flags, pictures of modern Turkey's founder, Mustafa Kemal Ataturk, and a banner reading: "The Turkish people are noble. They would never commit genocide", Anatolia news agency said.