Azerbaijan accused Armenia on Wednesday of trying to attack its gas and oil pipelines and warned of a "severe" response, as tensions mounted over a fraying ceasefire in the mountain enclave of Nagorno-Karabakh.
Armenia has denied targeting Azeri pipelines, which supply world markets with oil and gas, but concern is growing over the failure of a four-day-old ceasefire to end the worst fighting in decades over the tiny territory in the South Caucasus.
More than 500 people have been killed since the fighting broke out on 27 September in and around Nagorno-Karabakh, which is internationally recognised as part of Azerbaijan but is populated by ethnic Armenians.
The violence, which continued on Wednesday, has raised fears that big regional powers Turkey and Russia could be sucked into the conflict.
"Armenia is trying to attack and take control of our pipelines," Azeri President Ilham Aliyev said in an interview with Turkish broadcaster Haberturk.
"If Armenia tries to take control of the pipelines there, I can say that the outcome will be severe for them," he said.
Azerbaijan's defence ministry said separately that it would destroy all military facilities in Armenia that targeted Azeri civilian locations.
The Armenian defence ministry has denied firing on civilian targets, but said it reserved the right to target any military installations and combat movements in Azerbaijan.
Armenian Prime Minister Nikol Pashinyan was due to address the nation on Wednesday.
Ceasefire accusations
Armenia and Azerbaijan accused each other of new violations of the humanitarian violations on Wednesday morning, and each accused the other of shooting first.
The ceasefire was meant to allow the sides to swap prisoners and bodies of those killed but the continued fighting has hindered those efforts.
The defence ministry in Nagorno-Karabakh accused Azeri forces of launching artillery and rocket attacks in several areas.
Defence officials in the enclave said their forces had shot down an Azeri Su-25 fighter jet but Azerbaijan denied this.
Azerbaijan's defence ministry accused Armenian forces of new attacks on Azeri army positions along the line of contact that divides the two sides, and that the Terter, Aghdam and Aghjabedi regions inside Azerbaijan were under artillery fire.
The Azeri prosecutor's office reported one new civilian death and several wounded, including Azeri journalists.
Russian Defence Minister Sergei Shoigu spoke to the Azeri and Armenian defence ministers by phone, and urged the two former Soviet republics to observe the ceasefire.
Tension is growing between Russia, which has a defence pact with Armenia, and Turkey, an ally of Azerbaijan.
Moscow has been particularly alarmed by Turkey and Azerbaijan suggesting the conflict could be resolved militarily.
"It is not a secret that we cannot agree with a statement that a military solution to the conflict is permissible," Russian Foreign Minister Sergei Lavrov told local radio stations.
Mr Lavrov said it would be right to deploy Russian military observers on the line of contact that divides the sides in Nagorno-Karabakh, but that it was up to Azerbaijan and Armenia to decide.
A Russian attempt to broker a cease-fire to end the worst outbreak of hostilities over the region of Nagorno-Karabakh has failed to get any traction Source: IHA
The fighting in one of the former Soviet Union's "frozen conflicts" is the worst since a 1991-94 war over Nagorno-Karabakh that killed about 30,000 people.
Nagorno-Karabakh officials said on Tuesday that 532 servicemen had been killed since fighting flared on 27 September.
They did not immediately update the death toll on Wednesday.
The latest death reported by Azerbaijan's prosecutor general appeared to take the toll to 43 Azeri civilian deaths since 27 September.
Azerbaijan has not disclosed military casualties.
