Cross-border raids have led to the deaths of five Azerbaijani soldiers by Armenian troops, just one day after three Armenians were killed along the tense border between the two ancient enemies.

Azerbaijan’s defense ministry accused an Armenian sabotage group” of carrying out the killings. In response, the Armenian defense ministry said its personnel were simply reacting to an attempted illegal border-crossing by Azerbaijani forces.

Armenia and Azerbaijan have engaged in repeated tit-for-tat killings and skirmishes ever since the 1994 ceasefire following the conflict over the disputed Nagorno-Karabakh region.

Nagorno-Karabakh, which lies entirely within Azerbaijan, was taken over by Armenian forces during the 1988-1994 war that killed about 30,000 people and displaced 1 million others.

Technically, Armenia and Azerbaijan remain at war since there was a never a comprehensive final peace agreement between the two parties.

Nagorno-Karabakh has a majority Armenian population, although Azerbaijan claims it as its own and has repeatedly threatened military force to seize the region. Armenia has in turn vowed a full-scale war if Azerbaijan tried such a military adventure in Nagorno-Karabakh.

The resumption of violence comes as U.S. Secretary of State Hilary is visiting the southern Caucasus region to urge for peace.

I am very concerned about the danger of escalation of tensions and the senseless deaths of young soldiers and innocent civilians, Clinton said on Monday after meeting with Armenia's president Serzh Sarkisyan and foreign minister, Edward Nalbandian.

The use of force will not resolve the Nagorno-Karabakh conflict and therefore force must not be used. And we are calling on everyone to renounce force as well as refraining from violence. I assured the president that I would make these points in Baku [Azerbaijan].”

Warning that a worsening Azeri-Armenian conflict could spark wider problems in the region, Clinton said that the US, in tandem with Russia and France, would seek to mediate peace.

After visiting with top government officials in Armenia on Monday, Clinton is spending Tuesday in Georgia. On Wednesday, the secretary will journey to Azerbaijan.