Azerbaijan's defense ministry says it has started an anti-terrorism operation in Nagorno-Karabakh, the region at the center of a decades-long dispute with Armenia.

The ministry said on Tuesday that the operation had started to "disarm and secure the withdrawal of formations of Armenia's armed forces from our territories and neutralize their military infrastructure."

The ministry accuses the Armenian side of carrying out terrorism in Nagorno-Karabakh, saying a landmine explosion led to civilian deaths.

An Armenian human rights group says the operation has killed 27 people, including two civilians, with over 200 people injured.

Russia, an ally of Armenia that brokered a ceasefire between the two sides in 2020, is expressing concern.

Kremlin spokesperson Dmitry Peskov said on Tuesday that the important thing is to persuade Armenia and Azerbaijan to sit down at the negotiating table.

In a televised address, Armenian Prime Minister Nikol Pashinyan accused Azerbaijan of starting a "ground operation aimed at ethnic cleansing." Pashinyan expressed hope that Russian peacekeepers in the region will fulfill their responsibilities.

Russian media report that he spoke with US Secretary of State Antony Blinken by phone, and they called for the use of "international de-escalation mechanisms."

Fighting in Nagorno-Karabakh in 2020 left more than 5,600 people dead. The conflict ended with de facto defeat of Armenia, and Russia mediating a ceasefire.

But analysts say Russia's invasion of Ukraine has weakened Moscow's influence on the dispute.