Azerbaijan and Armenia have defied calls for a ceasefire after the worst fighting in decades between the two over disputed territory.
Emmanuel Macron, Vladimir Putin and Donald Trump put out a joint statement as co-chairs of the Organisation for Security and Co-operation in Europe's Minsk Group, which seeks to find a peaceful solution to the Nagorno-Karabakh conflict.
They "condemn in the strongest terms the recent escalation of violence along the Line of Contact in the Nagorno-Karabakh conflict zone," the statement said.
But Turkey - an ally of Azerbaijan - dismissed demands for a ceasefire.
Nagorno-Karabakh is officially part of Azerbaijan but governed by separatist ethnic Armenians. Years of negotiations have never resulted in a peace treaty.
Azerbaijan and Armenia fought a war in 1988-94 over the territory. Armenia backs the self-declared republic but has never officially recognised it.
Heavy shelling persisted overnight in the region's main city, despite mounting international concern.
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