Azerbaijan did not confirm the truce, which would bring to an end the deadliest exchanges between the countries since 2020.
The clashes were linked to a decades-old dispute between the former Soviet states.
Russia is the pre-eminent diplomatic force in the region and maintains 2,000 peacekeepers there. Moscow brokered the deal that ended the 2020 fighting, in which hundreds died.
“Thanks to the involvement of the international community, an agreement has been reached on a ceasefire,” Armen Grigoryan, secretary of Armenia's Security Council, told Armenian television, according to Russian news agencies.
The announcement said the truce had been in effect for several hours. Armenia's defence ministry had earlier said that shooting in border areas had stopped.
Each side blamed the other for the clashes.
Armenian Prime Minister Nikol Pashinyan had previously told Parliament that 105 Armenian servicemen had been killed since the violence began this week.
Azerbaijan upped their death toll from 50 to 75 in the two days of fighting.
Grigory Karasin, a senior member of Russia's upper house of Parliament, told the RIA news agency that the truce was clinched largely through Russian diplomatic efforts.
Kremlin leader Vladimir Putin had spoken to Mr Pashinyan, he said. Mr Putin appealed for calm after the violence erupted and other countries called for restraint on both sides.
In his address to parliament, Mr Pashinyan had said his country had appealed to the Moscow-led Collective Security Treaty Organisation to help to restore its territorial integrity.
“If we say that Azerbaijan has carried out aggression against Armenia, it means that they have managed to establish control over some territories,” Russia's Tass agency quoted him as saying.
Armenia and Azerbaijan have been fighting for decades over Nagorno-Karabakh, a mountainous enclave recognised as part of Azerbaijan while being home to a large Armenian population.
Fighting first erupted towards the end of Soviet rule. Armenian forces took control of large areas of territory in and around it in the early 1990s. Azerbaijan, backed by Turkey, largely retook those territories over six weeks in 2020.
Skirmishes have since erupted periodically despite meetings between Mr Pashinyan and Azerbaijani President Ilham Aliyev aimed at clinching a comprehensive peace settlement.
Domestic unhappiness in Armenia about the 2020 defeat has prompted repeated protests against Mr Pashinyan, who dismissed reports he had signed a deal with Baku.
In a Facebook post, he blamed the reports on “informational sabotage directed by unfriendly forces”.
A full-fledged conflict would risk dragging in Russia and Turkey, and destabilise an important corridor for oil and gas pipelines at a time when war in Ukraine is disrupting energy supplies.
Azerbaijan accused Armenia, which is in a military alliance with Moscow and home to a Russian military base, of shelling its army units.
US Secretary of State Antony Blinken said on Tuesday that Russia could either “stir the pot” or use its influence to “calm the waters”.