Russia on Saturday accused Azerbaijan of violating the Moscow-brokered cease-fire that ended a 2020 war with Armenia by letting its troops cross over the demarcation line.
Arch foes Baku and Yerevan have been locked for decades in a territorial conflict over Azerbaijan's Armenian-majority region of Nagorno-Karabakh.
The fragile Russian-mediated truce, which ended six weeks of fighting in autumn 2020, has stood despite occasional shootouts along the Armenian-Azerbaijani border and in Karabakh.
"On March 25 … a unit of the armed forces of Azerbaijan crossed a line of contact in the district of Shusha, in violation" of the agreement of November 9, 2020, the Russian defense ministry said in a statement.
It said Russian peacekeepers "are taking measures aimed at preventing escalation … and mutual provocations."
'Necessary control measures'
Earlier on Saturday, Azerbaijan's defense ministry said it had taken control of some auxiliary roads in Karabakh.
The ministry said "necessary control measures were implemented by the units of the Azerbaijan army in order to prevent the use of the dirt roads north of Lachin" for arms supplies from Armenia.
The sole road linking Karabakh to Armenia, the Lachin corridor, has for months been under Azerbaijani blockade, which Yerevan says has led to a humanitarian crisis in the enclave and is aimed at driving Armenians from Karabakh.
Baku has denied the claims.
Last week, Armenian Prime Minister Nikol Pashinyan warned against a "very high risk of escalation" in Karabakh.
Armenia has also accused Russian peacekeepers of failing to protect ethnic Armenians living in the restive region.
Yerevan has said it would appeal to the international community to help prevent genocide in Nagorno-Karabakh.
On Thursday, Armenia accused Azerbaijani troops of killing an Armenian soldier along the countries' volatile frontier.
Last week, Azerbaijan accused Armenia of opening fire on its army positions along the border and in Karabakh.
Pashinyan and Azerbaijani President Ilham Aliyev have held several rounds of peace talks mediated by the European Union and the United States.
Last week, Pashinyan noted some progress in the peace process, but said "fundamental problems" remain because "Azerbaijan is trying to put forward territorial claims, which is a red line to Armenia."
Yerevan has accused Baku forces of occupying about 150 square kilometers in Armenia, along the countries' shared border, after the 2020 war.
The European Union last month deployed an expanded monitoring mission to the Armenian side of the border as Western engagement grows in a region that is traditionally the Kremlin's sphere of influence.
When the Soviet Union collapsed in 1991, ethnic Armenian separatists in Karabakh broke away from Azerbaijan. The ensuing conflict claimed some 30,000 lives.