Baku (AFP) - Azerbaijan said Friday eight soldiers had been killed in three days of clashes with arch-foe Armenia on the border and near the disputed Nagorny Karabakh region as tensions spiked in the long-running conflict.

International mediators, who have for years sought to help the two countries reach a breakthrough, expressed concern over the violence, with the United States renewing a plea for the presidents from both countries to meet for talks.

Azerbaijan's defence ministry said Armenian troops had ramped up their activity in the past few days and attacked Azeri positions.

"Reconnaissance and sabotage groups of the Armenian armed forces attempted to break through the line of contact between the troops along the entire front line," the ministry said, adding that the Armenian troops had been repelled.

"As a result of clashes over the past three days, eight Azeri troops have died," it said.

Azerbaijan and Armenia have been locked in a protracted conflict over the Nagorny Karabakh region with occasional skirmishes along the front.

The latest clashes however represent a surge in tensions between the two countries, with one prominent Azeri military expert saying Baku has not suffered such losses in a single bout of hostilities since 1994.

Azerbaijan said Armenia had also suffered losses, although it did not provide any details.

In Armenia, a high-ranking defence ministry official presented a different version of the events.

Speaking to AFP, he said Azerbaijani "sabotage groups" had tried to break into Armenia and that the Azeris had lost 14 troops in the latest skirmish.

"Azerbaijani subversive groups were ambushed," the official said. "As a result, they have 14 dead and lots of wounded. There are no casualties or wounded on the Armenian side."

Officials in Nagorny Karabakh for their part said two Armenian troops died in an attack by Azerbaijani forces on Thursday.

Armenian-backed separatists seized Nagorny Karabakh from Azerbaijan in a 1990s war that killed 30,000 people.

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Despite years of negotiations since a 1994 ceasefire, the two sides have yet to sign a peace deal.

- No military solution -

US officials said Washington was concerned about the escalation of violence, calling "on the sides to take immediate action to reduce tensions and respect the ceasefire."

"There can be no military solution to the conflict. Retaliation and further violence will only make it more difficult to bring about a peaceful settlement," said deputy State Department spokeswoman Marie Harf in a statement.

She added US officials "stand ready to help efforts to bring about a lasting settlement."

Azerbaijan has threatened to take back the disputed region by force if negotiations do not yield results, while Armenia has vowed to retaliate against any military action.

Uzeir Dzhafarov, a prominent military expert in Azerbaijan, said clashes had recently intensified between the two sides.

"Azerbaijan has not had such losses since March 1994," he told AFP.

A security analyst in Armenia, Stepan Safaryan, for his part pointed out that the clashes came as international mediators tried to organise a meeting between the leaders of Armenia and Azerbaijan.

Safaryan suggested that the leadership of Azerbaijan had sought to wring concessions from Armenia in the run-up to the meeting.

"Through such an escalation Azerbaijan is blackmailing the international community and the Armenian side before the meeting," he told AFP.

The Karabakh peace talks are mediated by the so-called OSCE Minsk Group, which is co-chaired by France, Russia and the United States.