Russia on Saturday expressed concerns about clashes between the Armenian and Azerbaijani armed forces in the disputed territory of Nagorno-Karabakh that have left 13 dead on the Azerbaijani side in recent days.

"We're expressing our concern over the sharp deterioration of the situation in the conflict zone," Maria Zakharova, spokesperson for Russia's Foreign Ministry, told local news agencies.

She said "a major escalation is unacceptable" and denounced the fighting as "a serious violation of cease-fire accords and the declared intentions of solving the dispute by political means."

"We urge all involved in the conflict to show restraint, renounce the use of force and take urgent measures to stabilize the situation," Zakharova added.

In 2010, Russia signed an agreement with Armenia that extends its lease on a military base in that country until 2044, while also pledging to safeguard Armenia - which is located between Turkey and Iran - from external threats.

Azerbaijan and Armenia have accused one another in recent days of carrying out attacks and making incursions into Nagorno-Karabakh, which lies within Azerbaijan but is populated mainly by ethnic Armenians.

Azerbaijan's Defense Ministry said four of the country's soldiers were killed Saturday in border clashes with Armenia, raising the number of Azerbaijani troops who have died over the past 48 hours to 13.

The eight soldiers killed on Thursday represent the biggest single-day death toll for Azerbaijani troops since a cease-fire was declared in May 1994, military expert Dzhasura Sumerinli told Efe.

The Organization for Security and Co-Operation in Europe has been supervising that truce since then.

For its part, Armenia threatened Saturday to carry out punitive measures against Azerbaijan's military forces if the neighboring country does not cease its incursions into the separatist enclave.

The conflict in Nagorno-Karabakh goes back to the collapse of the Soviet Union, when the region's Armenian population sought unification with Armenia, leading to a 1991-1994 war that left more than 25,000 people dead.

Nagorno-Karabakh and Armenian troops occupy the entire enclave and seven adjacent districts and have created a "security buffer" that represents a third of Azerbaijani territory. EFE