Two white doves that were released by children standing alongside Pope Francis as a peace gesture have been attacked by other birds.

As tens of thousands of people watched in St. Peter's Square on Sunday, a seagull and a large black crow swept down on the doves right after they were set free from an open window of the Apostolic Palace.

One dove lost some feathers as it broke free from the gull. But the crow pecked repeatedly at the other dove.

It was not clear what happened to the doves as they flew off.

While speaking at the window beforehand, Francis had appealed for peace in Ukraine, where anti-government protesters have died.

Pope Francis has called for "constructive dialogue" between Ukraine's authorities and its people, urging all to renounce violence in the upheaval convulsing their country.

Francis said he was praying for Ukraine, especially for those who have lost their lives in recent days. He appealed on Sunday for "the spirit of peace and the search for the common good" to prevail in the eastern European nation.

Weeks of protests have escalated into violent clashes between police and demonstrators angry that the government didn't sign a deal to bring it closer to the European Union and accepted Russian aid instead.