By Hasmik Mkrtchyan

YEREVAN (Reuters) - Armenia's main opposition party said on Monday the country's president had rigged the result of a February poll and it called on the Constitutional Court to rule that it had been the winner.

Incumbent President Serzh Sarksyan was declared the victor with 58.6 percent of the vote, against 37 percent for opposition leader Raffi Hovannisian.

"We demand to register the people's victory and to declare Raffi Hovannisian Armenia's president," Hovsep Khurshudyan, spokesman for the Heritage Party, told reporters after submitting an appeal to the court.

The court has 10 days to give its ruling. Armenia's central election commission said last month there were no legal violations during the vote that could have influenced results.

International election monitors said the poll was an improvement from previous ones but that it still lacked real competition after some of Sarksyan's adversaries decided not to run, fearing the results would be skewed.

Since the February 18 poll, the opposition has organized a series of peaceful rallies to protest against alleged vote rigging.

Investors worry over any signs of instability in the South Caucasus state, where 10 people were killed in violence that followed Sarksyan's initial election in 2008.

Another candidate, Andrias Ghukasyan, who went on hunger strike at the start of the campaign to protest against the organization of the vote, also submitted a complaint to the Constitutional Court.

Armenia's central election commission said last month there were no legal violations during the vote that could have impacted results.

Hovannisian, a U.S.-born former foreign minister of the landlocked ex-Soviet republic, submitted 70 complaints to the electoral commission, which said last week that the documents were based neither on facts nor legal evidence.

Armenia, a country of 3.2 million people, hosts one of Russia's few foreign military bases and is part of a post-Soviet security alliance dominated by Moscow. It borders Iran, Georgia, Turkey and Azerbaijan.

(Writing by Margarita Antidze; Editing by Stephen Powell)