Clashes erupted between Azerbaijani and Armenian troops early on Tuesday in a resumption of decades-old hostilities linked to the disputed territory of Nagorno-Karabakh.
Azerbaijan, which re-established full control over the territory in a six-week conflict in 2020, acknowledged casualties among its forces, according to reports published by Reuters.
In a speech to Armenia's parliament, Armenia's Prime Minister Nikol Pashinyan said 49 Armenian service personnel died during overnight clashes. Pashinyan said Baku had attacked Armenia's positions overnight and that fighting was ongoing.
Nikol Pashinyan accused Azerbaijan of attacking Armenian towns because it did not want to negotiate over the status of Nagorno-Karabakh, an enclave that is inside Azerbaijan but mainly populated by ethnic Armenians.
"The intensity of hostilities has decreased but attacks on one or two fronts from Azerbaijan continue," Pashinyan said in a speech to parliament, according to Russian media.
Azerbaijan, which accused Armenia of carrying intelligence activity along the border and moving weapons, said its military positions came under attack by Armenia.
Nagorno-Karabakh, a mountainous region of the South Caucasus, is internationally recognised as part of Azerbaijan, but the local ethnic Armenian residents reject Baku's sovereignty over the region. It has been the source of fierce tensions between the two countries for decades.
Azerbaijan and Armenia agreed a ceasefire early on Monday to halt a flare-up in hostilities over the Nagorno-Karabakh region, but it fell apart minutes later, Azerbaijani media said.
A ceasefire agreement came into force at 9 am local time (0500 GMT), according to media reports and a source, who asked not to be named. But Azerbaijani media reported that it was broken soon after.
Tensions flared overnight in the latest escalation of decades-old hostilities between the two countries in the south Caucasus over control of the disputed region.
Azerbaijani media said the ceasefire broke down within 15 minutes.
US Secretary of State Antony Blinken has expressed deep concern about reports of attacks along the Armenia-Azerbaijan border. He called for an immediate end to hostilities.
"As we have long made clear, there can be no military solution to the conflict," Blinken said in a statement. "We urge an end to any military hostilities immediately."
Russia called on Armenia and Azerbaijan to cease hostilities and observe a ceasefire agreement on Tuesday, expressing "extreme concern" over renewed fighting between the two countries.
In a statement, Russia's foreign ministry said it had brokered a ceasefire at 0900 Moscow time (0600 GMT) this morning and it expected both sides to fulfill the terms of the agreement.
"We express our extreme concern over the sharp aggravation of the situation in areas of the Armenian-Azerbaijani border," the foreign ministry said.
"We call on the sides to refrain from further escalation of the situation, exercise restraint and strictly observe the ceasefire."
Turkey said on Tuesday it continued to back Azerbaijan and called on Armenia to "cease its provocations" after clashes erupted between the two South Caucasus countries that resumed decades-old hostilities.
Turkish Defence Minister Hulusi Akar held talks with Azeri counterpart Zakir Hasanov, the ministry said. "He emphasised that Turkey has always stood by brotherly Azerbaijan and will continue to stand by it in its just causes," it said.
