Azerbaijan says one of its generals and five other officers have been killed in a third day of fighting with Armenian forces on the countries' border. An Azeri private also died, bringing the Azeri death toll so far to 11. Armenia says four of its troops - two of them officers - were killed. Both countries were part of the Soviet Union until its collapse in the 1990s. They fought a bloody war over a mountainous territory, in a dispute that remains unresolved. Nagorno-Karabakh is internationally recognised as part of Azerbaijan but is controlled by ethnic Armenians. This clash, however, took place north of this disputed territory. Azerbaijan says heavy fighting is continuing in Tovuz district, bordering on Tavush in north-eastern Armenia. Dmitry Peskov, spokesman for Russian President Vladimir Putin, said Russia was "deeply concerned" about the outbreak of violence and was willing to mediate. "We urge both parties to show restraint and to comply with their obligations under the ceasefire." A US state department release on Monday said the country "condemns in the strongest terms the violence along the Armenia-Azerbaijan international border" and called on both sides to stop the fighting and abide by the ceasefire.