United Nations Secretary-General Antonio Guterres urged Azerbaijan and Armenia on Monday to exercise maximum restraint after border clashes between the long-feuding former Soviet republics.

"The secretary-general is following with deep concern the current tensions between Azerbaijan and Armenia. He calls for maximum restraint, as a full conflict between these two countries would be disastrous," U.N. spokesman Stephane Dujarric said.

Russia, which has a military base in Armenia, has urged the two sides to cease fire and show restraint. The Kremlin has said Moscow is ready to act as a mediator.

International concern is heightened because of the threat to stability in a region serving as a corridor for pipelines taking oil and gas from the Caspian Sea to global markets.

Last Sunday, the Armenian army attempted to attack Azerbaijani positions with artillery fire toward the northwestern Tovuz border district, withdrawing after suffering losses following retaliation from the Azerbaijani military.

Azerbaijan has blamed Armenia for the "provocative" actions, with Turkey throwing its weight behind Baku and warning Yerevan that it would not hesitate to stand against any kind of attack on its eastern neighbor.

The Armenian military had since 1991 illegally occupied the Nagorno-Karabakh region, an internationally recognized territory of Azerbaijan.

Four U.N. Security Council and two U.N. General Assembly resolutions, as well as decisions by many international organizations, refer to this fact and demand the withdrawal of the occupational Armenian forces from Nagorno-Karabakh and seven other occupied regions of Azerbaijan.