Dozens of soldiers have been killed in fighting between neighbouring countries Armenia and Azerbaijan.
Armenia's Prime Minister Nikol Pashinyan said 49 of its soldiers died in overnight clashes.
The two countries have fought two wars and seen regular smaller clashes over the course of three decades.
Russia said it brokered a ceasefire for the latest outbreak. Armenia initially said only that the fighting had calmed, rather than ended completely.
Later, Azerbaijan said it had completed its objectives following "provocations" from its neighbour.
At the core of the dispute is the region of Nagorno-Karabakh. It is, according to internationally-recognised borders, firmly a part of Azerbaijan - but is populated by ethnic Armenians.
The cultural divide extends beyond politics into religion, too: Armenia is a majority-Christian country, while Azerbaijan is mostly Muslim.
Both countries were part of the Soviet Union before its dissolution at the end of 1991.
The dispute has led to full-scale war in the 1980s and 1990s, a six-week war in 2020 and continuing clashes for decades.
The two countries blame each other for the latest outbreak of violence.
Armenia claimed that several towns along the border had been shelled by its neighbour and that it had responded to the provocation.
Azerbaijan said its infrastructure came under attack first, with military spokesman Lt Col Anar Eyvazov saying that military movements over the past month "demonstrate that Armenia is preparing for a large-scale military provocation".
Violence continued on Monday night before Moscow said it had negotiated a rapid ceasefire to take effect early on Tuesday morning.
Armenia's N ikol Pashinyan, however, said "the intensity of hostilities has decreased, but attacks on one or two fronts from Azerbaijan continue".
Azerbaijan is understood to have also suffered casualties, but has not publicly issued a statement on the number of injured or dead.
The fighting has been condemned internationally. US Secretary of State Antony Blinken made personal phone calls to the leaders of both nations on Tuesday, urging them to come to a peaceful settlement and prevent further fighting.
Russia is close to Armenia, but is a major power in the region and maintains relationships with both sides.
"The president is naturally making every effort to help de-escalate tensions at the border," he said.
Turkey, meanwhile, has ties with Azerbaijan and seemingly backed its version of events. Turkey's foreign minister Mevlut Cavusoglu, said "Armenia should cease its provocations and focus on peace negotiations".
Monday night's fighting is believed to be the worst since the 2020 conflict, in which thousands were killed. That war ended in a deal brokered by Russia, which saw Armenia withdraw its troops from occupied areas around Nagorno-Karabakh.
A Russian peacekeeping force of nearly 2,000 men was deployed to the area as part of the negotiations, where it remains today.
https://www.bbc.com/news/world-europe-62888891
