YEREVAN, April 16 (Reuters) - Azerbaijan must accept that its breakaway Nagorno-Karabakh region is an independent republic that will never be returned to Azeri control, Armenia's president said on Wednesday.

Nagorno-Karabakh, in the Caucasus mountains, broke away from Azerbaijan as the Soviet Union fell apart, sparking a war which killed about 35,000 people. A ceasefire was agreed in 1994 but the search for a lasting peace is stalled.

The region's ethnic Armenian separatists run their own affairs, with support from Armenia. The region has declared its independence from Azerbaijan, but this has not been recognised by any state.

"Azerbaijan must understand the simple reality that the existence of the republic of Nagorno-Karabakh's independence is irreversible," President Serzh Sarksyan, who was sworn in this month, said in comments supplied by his press service.

"It is impossible to even imagine that the Republic of Nagorno-Karabakh could be subordinate in any way to Azerbaijan," said Sarksyan, who is a native of the region.

"The people of Nagorno-Karabakh have won their right to a free and independent life. And through our efforts, that right must be recognised by the international community."

Azerbaijan says Armenia has illegally occupied Nagorno-Karabakh, and a number of Azeri districts surrounding the region.

Baku, which announced a 53 percent rise in military spending this month, says it is committed to stalled peace talks but has refused to rule out using force to restore its control.

Azerbaijan and Armenia are still officially at war and their troops frequently fight skirmishes along a heavily mined front line. Up to 16 soldiers were killed in a clash earlier last month.

Russia, the United States and France are mediators in the conflict. (Reporting by Guy Faulconbridge, editing by Richard Balmforth)

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