The truce, brokered by Russia last week, stipulated that Armenia hand over control of some areas its holds outside Nagorno-Karabakh’s borders to Azerbaijan.
Video showed troops and armored vehicles moving into the district of Aghdam, which Armenia conceded in the controversial armistice, just a day after columns of its soldiers and tanks rolled out of the territory.
Armenia will also hand over the Kalbajar district wedged between Nagorno-Karabakh and Armenia on 25 November and the Lachin district by December 1.
As part of last week’s peace deal, Armenia agreed to return 15% to 20% of the Nagorno-Karabakh territory captured by Azerbaijan in recent fighting, including the historical town of Shusha.
The exchange of territory was originally due to begin on Sunday, with Armenians in the Kalbajar district fleeing en masse before the official deadline for Azerbaijan’s takeover.
But Azerbaijan’s President Ilham Aliyev postponed the deadline by one week over “humanitarian” considerations.
The Russian peacekeeping force of 2,000 troops has deployed to the administrative center of the region, Stepanakert, and set up checkpoints and observation posts along the strategic Lachin corridor connecting Nagorno-Karabakh with Armenia.
On Thursday, Armenian residents of Aghdam hurriedly picked pomegranates and persimmons from trees surrounding their homes and packed vans with furniture, before fleeing ahead of the official deadline to cede the mountainous province.
Tens of thousands of Azerbaijanis are expected to return to the region. On Friday, Azerbaijan quickly organized prayers at a local mosque to signal the return of the city to the control of the mostly-Muslim nation.
Nagorno-Karabakh lies within Azerbaijan but has been under the control of ethnic Armenian forces backed by Armenia since a separatist war there ended in 1994. That war left not only Nagorno-Karabakh itself but substantial surrounding territory in Armenian hands.
Heavy fighting that flared up Sept. 27 marked the biggest escalation of the decades-old conflict between the two ex-Soviet nations in over a quarter-century, killing hundreds and possibly thousands of people.
The truce last week halted the violence after several failed attempts to establish a lasting cease-fire. It was celebrated as a victory in Azerbaijan, but sparked mass protests in Armenia, with thousands regularly taking to the streets to demand the ouster of Prime Minister Nikol Pashinyan.
On Friday, several Armenian news sources reported that Defense Minister David Tonoyan had tendered his resignation in what, if confirmed, would be another exit of a high-ranking official from his cabinet. The country’s foreign minister resigned earlier this week and President Armen Sarkisian had called for Pashinyan to step down and allow snap elections to lead the country out of the crisis.
Pashinyan has responded with calls for unity and has issued a government roadmap out of the crisis that include returning refugees to the Karabakh region, which Armenia calls Artsakh, and modernizing the country’s military. He has called for greater development in Stepanakert and those territories remaining under Armenian control.
AP and The Guardian contributed to this story.