Nagorno-Karabakh remains gripped by fighting as Washington and Moscow call for restraints. At least 13 have been killed in the third day of fighting over the disputed territory controled by ethnic Armenian separatists.
Azerbaijan's defense ministry warned Monday that it would launch a "full-scale operation" if Armenian forces continued "provocations."
This comes as Armenian President Serzh Sarkisian said a "ceasefire would only be possible if the militaries of both sides return to the positions" they held prior to the outbreak of hostilities.
Energy-rich Azerbaijan has threatened to take back the breakaway region. Armenia says it could crush any offensive.
World leaders appeal for calm
The French foreign ministry issued a statement on Monday saying that mediators from both sides would meet in Vienna on Tuesday to discuss the tensions. Russian Foreign Minister Sergei Lavrov and US Secretary of State John Kerry discussed the crisis in a phone conversation Monday, Russia's foreign ministry said.
The Armenian president is scheduled to visit German Chancellor Angela Merkel on Wednesday, with the talks expected to focus on the heightened tensions.
But Turkey - a close Azerbaijan ally - threw its rhetorical weight behind Baku. Turkish President Recep Tayyip Erdogan insisted that the Armenian-controlled region would "one day" return to Azerbaijan's control.
"We are today standing side-by-side with our brothers in Azerbaijan. But this persecution will not continue forever," Erdogan said in televised remarks.
Claim and counterclaim
Clashes had flared on Saturday and left a boy and at least 30 soldiers on both sides dead, making it the worst fighting since a full-scale war in 1994.
In Yerevan, the Armenian defense ministry said Karabakh rebels had advanced "at certain sectors" and had taken up new positions on the front line.
Armenian ministry spokesman Artsrun Hovhannesyan said an Azeri army unit had been "fully destroyed" in the conflict zone's southern flank.
Azerbaijan's defense ministry said its forces were ready with "all kinds of weapons" and described the rebel claim of having advanced as "untrue."
Azeri ministry spokesman Vagif Dargyahkly told The Associated Press that rebels had shelled front-line villages, despite a ceasefire announced unilaterally by the government in Baku.
Armenia and Azerbaijan continue to trade blame for the violence, which broke out Friday night. It has been the worst fighting in the area since the countries agreed to a ceasefire in 1994.
For years, the heavily militarized contact line that separated Azeri and separatist forces had remained static, with the exception of intermittent exchanges of gunfire and occasional casualties.
ipj, jar/msh (AFP, AP, Reuters)