The Romanian People's Salvation Cathedral will be the tallest in the world but its cost has been criticised in a country where many people live in poverty.
It was inaugurated in a ceremony on Sunday attended by tens of thousands of worshippers from all over the country as well as ethnic Romanians living in Ukraine.
Local reports described huge crowds congregating in front of the building site to follow the ceremony on screens outside and three people were hospitalised when scuffles broke out between riot police and Orthodox believers.
The service was led by Bartholomew I, the Ecumenical Patriarch and Archbishop of Constantinople-New Rome, and the Romanian patriarch, Daniel.
The consecration mass marked 100 years since the creation of modern-day Romania.
Work started on the cathedral in 2010 and it is due to be completed in 2024.
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