MOSCOW, MAY 27 -- Soviet troops shot and killed six armed vigilantes today during a brief but furious gun battle at the railroad station in the Armenian capital that also left 10 soldiers and a passerby wounded, the Soviet news agency Tass reported.

Tass said the soldiers had just returned to Yerevan from escort duty aboard a train to the nearby Azerbaijani province of Nakhichevan when a group of about 15 armed men opened fire on them. The troops immediately returned fire, Tass said, killing five of the gunmen and wounding two others, one of whom died at a hospital later. At least three of the wounded soldiers were in critical condition, the news agency said.

But the sketchy Tass account was disputed by a journalist at the Armenian news agency Armenpress, who said the shooting began after a peaceful crowd had gathered around the soldiers in an attempt to persuade them to leave Yerevan. He quoted a Soviet officer at the scene as saying the troops opened fire because they thought the crowd was about to seize their weapons.

Tass said the soldiers were exercising their right to use weapons in self-defense when they returned fire from the gunmen, whose political identity was not disclosed in the agency's brief dispatch.

While few details of the shootout were available, it was clearly the most serious incident of armed violence in Armenia since militant nationalist groups there began forming private armies early this year following the outbreak of virtual civil war with neighboring Soviet Azerbaijan. Soviet army and internal security troops have been attempting to confiscate arms from both Armenian and Azerbaijani vigilantes without much success over the past few months.

More than 300 people have been killed in Soviet ethnic violence so far this year, most of them in armed clashes involving Armenians, Azerbaijanis and Soviet internal security forces trying to maintain peace between the two ethnic groups, whose bloodletting was sparked three years ago by a dispute over control of Nagorno-Karabakh, a largely Armenian-populated enclave surrounded and administered by Azerbaijan.

Three days ago, militants fired on soldiers standing guard at military checkpoints in Nagorno-Karabakh, an attack that Tass said left one soldier and one vigilante dead. Tonight's railroad station gun battle in Yerevan comes on the eve of unofficial rallies planned in the Armenian capital Monday to mark the anniversary of Armenia's declaration of independence from Russia in 1918. Soviet troops occupied Armenia two years later, and the republic was subsequently incorporated into the Soviet Union.

Both Armenians and Azerbaijani activists stole large amounts of weapons from Soviet military units in January when fighting flared up along the borders of the two republics. Kremlin authorities responded to the open warfare by imposing martial law along the frontier and in the Azerbaijani capital, Baku, where ethnic Armenians were being killed by rioters, but have refrained from taking similar action in Yerevan.

The Armenian national movement, which is campaigning for Armenian annexation of Nagorno-Karabakh, has split into competing factions over the past few months, each with its armed offshoot. Weapons in the hands of the nationalists are known to include artillery, armored cars and even a tank.

Tension in Armenia has been rising for several days following republic-wide elections that were extended to include Nagorno-Karabakh despite Moscow's insistence that the region is part of Azerbaijan. Two days ago, the general commanding internal security forces in Armenia described the situation there as "explosive."