Senior US officials arrived in Armenia amid growing fears of an exodus from Nagorno-Karabakh after Azerbaijan’s military operation to take control of the region that’s at the center of a decades-long conflict.

USAID Administrator Samantha Power and Acting Assistant Secretary of State for Europe and Eurasian Affairs Yuri Kim were in the capital Yerevan to “affirm US support for Armenia’s sovereignty, independence, territorial integrity, and democracy and to address humanitarian needs stemming from the recent violence in Nagorno-Karabakh,” the US embassy said in a Facebook post Monday.

Amid spiraling tensions between Yerevan and the Kremlin over the Nagorno-Karabakh crisis, Russia accused Armenian Prime Minister Nikol Pashinyan of “unacceptable attacks” after he criticized his Moscow-led allies for failing to aid the country against Azerbaijan.

“The Yerevan leadership is making a huge mistake by deliberately trying to demolish Armenia’s multifaceted and centuries-old ties with Russia and making the country hostage to the geopolitical games of the West,” the Foreign Ministry in Moscow said Monday in a statement.

The struggle for control of Nagorno-Karabakh, which has a largely Armenian population but is internationally recognized as part of Azerbaijan, has killed tens of thousands and turned more than 1 million into refugees. The region’s Armenian population declared independence as the Soviet Union collapsed and controlled the territory until Azerbaijan took part of Nagorno-Karabakh and reclaimed seven surrounding districts in a 2020 war with Armenia that ended when Russian President Vladimir Putin brokered a cease-fire.

More than 6,600 Armenians from Nagorno-Karabakh have entered Armenia from Azerbaijan as of 5.p.m Monday local time, the Armenian government said, as local media reported long lines of vehicles at the border.

Officials from Baku and Armenian representatives from Nagorno-Karabakh held a second round of talks Monday on integrating the territory into Azerbaijan as part of an agreement that ended last week’s fighting. Nagorno-Karabakh said it would “completely disarm” its defense forces and accept rule by Azerbaijan under the accord, opening a new phase in one of the world’s most intractable territorial disputes.

The US diplomats were meeting government officials in Yerevan as Azerbaijani President Ilham Aliyev held talks with Turkish leader Recep Tayyip Erdogan. They met in Azerbaijan’s exclave of Naxcivan, which borders Turkey, Armenia and Iran, as Erdogan backs Baku’s demand for a transport corridor across southern Armenia to connect to the territory.

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Armenia rejects the demand and the corridor isn’t part of the truce brokered by Putin, which provides only for an opening of borders and transport links between the two neighbors including to Naxcivan.

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While Aliyev has said he wants the Armenian population to stay after forcing last week’s surrender, many in Nagorno-Karabakh see little future there after decades of enmity between the two sides. Thousands displaced in the fighting are unable or unwilling to return to their homes.

Pashinyan has said he accepts Nagorno-Karabakh is part of Azerbaijan but wants security mechanisms to guarantee that its Armenian population can live safely. He’s said Armenia will take in its ethnic kin from Nagorno-Karabakh if necessary.

Aliyev told reporters at the talks with Erdogan that he’s confident the integration of Nagorno-Karabakh’s Armenian population into Azerbaijan will be successful.

(Updates with Russian Foreign Ministry in third, fourth paragraphs)