Russia is deploying troops to the disputed Nagorno-Karabakh region to form a force to uphold a resolution to end fighting between Azerbaijan and Armenia, state media report, citing the Russian military.
Russia intends to send 1960 peacekeepers, 90 armoured personnel carriers and 380 vehicles to the mountainous region, which had been the focus of intense fighting over the past month and a half.
"Il-76 military transport aircraft with Russian peacekeepers have taken off from the Ulyanovsk-Vostochny airfield," the Russian Defence Ministry said, referring to a base in central Russia, state news agency TASS reported.
The peace deal, agreed by Russia with Azerbaijan and Armenia, came after Russia's military revealed on Monday that a Russian attack helicopter had been shot down in Armenian territory near the border with Azerbaijan, killing two crew members.
Azerbaijan's military accepted responsibility for the incident and apologised to Russia.
Russia has maintained close ties with both Armenia and Azerbaijan since the Soviet era.
Russia has not specified why the attack helicopter was in southern Armenian territory, about 100 kilometres from Nagorno-Karabakh but also far from a Russian military base in northern Armenia.
Russia has a permanent military presence in Armenia as part of a post-Soviet alliance, the Collective Security Treaty Organisation, which does not include Azerbaijan.
Upholding the ceasefire deal, Armenia reported that "relative calm is being maintained from 6am," according to a statement by Armenian military spokeswoman Shushan Stepanyan.
"Active combat operations on the whole front line are suspended," Stepanyan said in a statement posted on her Facebook page.
Largely controlled by Christian Armenian forces for more than a quarter of a century, the Nagorno-Karabakh region is considered by the United Nations as part of predominantly Muslim Azerbaijan.
With more than 1000 people reported killed, the fighting was the deadliest between Azerbaijan and Armenia since they waged a war in the late 1980s and early 1990s as they transitioned into independent countries amid the Soviet dissolution.
Azerbaijan's leadership has said that a goal of the military engagement has been to enable the return of Azerbaijanis to Nagorno-Karabakh.
Armenia was forced to make territorial concessions to Azerbaijan under the peace deal, announced early on Tuesday.
Armenia was to cede control over the Kalbajar and Lachin districts, which border Armenia's undisputed territory.
Turkey, a close ally of Azerbaijan, hailed the agreement as a gain for Azerbaijan, according to Turkish Foreign Minister Mevlut Cavusoglu.
Azerbaijan has achieved an "important gain on the field and on the table," Cavusoglu said on Twitter, adding: "We will continue to be one nation, one spirit with our Azerbaijani brothers and sisters."
Russia emphasised that the peace deal did not entail any Turkish peacekeeping troops being deployed in Nagorno-Karabakh.
"The deployment of Turkish soldiers in Karabakh has not been agreed," Kremlin spokesperson Dmitry Peskov said in comments carried by TASS.
Azerbaijani President Ilham Aliyev said in a speech broadcast earlier on Tuesday that Azerbaijan would set up a peacekeeping centre with "Russian and Turkish soldiers on duty".
He said Turkey would play a role in monitoring the ceasefire.