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The Azerbaijani Defense Ministry said it was using "high-precision weapons on the front line and in depth" as part of the operation, which it said were "of a local character."
The operation was meant to "suppress large-scale provocations" and drive out what it said were Armenian troops.
Azerbaijan urged civilians to stay away from military facilities, saying it has been in touch with Armenian residents of the Karabakh region via text messages, loudspeakers and information leaflets.
It added that it has established humanitarian corridors and reception stations in several places, including the Lachin road, to ensure the population is evacuated from danger zones.
Meanwhile Russia, which has maintained a peacekeeping force in Nagorno-Karabakh since the end of a 2020 war, said it was in touch with various parties with regards to the situation, including Azerbaijan.
What happened before the operation?
Azerbaijan said that four soldiers and two civilian road workers were killed on Tuesday in landmine explosions in Nagorno-Karabakh that it blamed on "illegal Armenian armed groups."
Nagorno-Karabakh, which has a sizable ethnic Armenian population, has been partially under Baku's control since the 2020 war.
Azerbaijan has for months blocked the Lachin corridor, which connects the breakaway region to Armenia, under the pretext that it was used for arms smuggling.
On Monday, Azerbaijan allowed badly needed food and medicine into Karabakh, along two roads simultaneously, including Lachin.
Ongoing Armenia-Azerbaijan tensions
Long-contested since a separatist war ended in 1994, the Nagorno-Karabakh region has fueled fighting between neighboring Armenia and Azerbaijan. The region lies within Turkey-backed Azerbaijan but had largely been under the control of Yerevan-backed ethnic Armenian forces since 1994.
The six-week 2020 war brought areas of the region under Azerbaijan's control and ended with a Russia-brokered peace deal.
Tensions between Azerbaijan and Armenia have nevertheless remained high, with the two regularly exchanging fire across their highly-fortified, closed border. Meanwhile, both sides have sought to blame each other for the ongoing stand-off.
Armenia, which last month requested the UN Security Council convene an emergency meeting to address humanitarian conditions in Nagorno-Karabakh, says Azerbaijan is amassing troops.
In turn, Azerbaijan says it is being forced to take "urgent measures" to stop Karabakh forces from further fortifying the border.
rmt/jcg (AFP, Reuters)