The United States on Sunday expressed concern about the worsening situation in a disputed Azerbaijan enclave, calling for humanitarian supplies to be allowed through and declaring any use of force in the dispute with Armenia as "unacceptable."

"The United States is deeply concerned about the rapidly deteriorating humanitarian situation in Nagorno-Karabakh," said a statement from US Secretary of State Antony Blinken.

He called for the immediate opening of two supply routes to allow the passage of "desperately needed humanitarian supplies" to the Armenian-populated region and warned leaders against any provocation.

Nagorno-Karabakh on Saturday elected a new president as tensions spiraled between archrivals Azerbaijan and Armenia.

Lawmakers in the breakaway enclave voted overwhelmingly to elect security chief Samvel Shahramanyan, 45, to immediately succeed outgoing leader Arayik Harutyunyan.

Popular frustration with Harutyunyan's rule was growing amid food shortages after Azerbaijan closed the sole road linking Nagorno-Karabakh to Armenia.

But Azerbaijan called the election "a clear violation of Azerbaijan's sovereignty and territorial integrity" and a "flagrant violation of international law."

In recent months, Armenia and Azerbaijan have traded accusations of cross-border attacks.

Armenia has warned that Azerbaijan was massing troops on the countries' shared border and near Nagorno-Karabakh.

Blinken, in his statement, said the United States would "continue to strongly support efforts by Armenia and Azerbaijan to resolve outstanding issues through direct dialogue, with the aim of achieving a dignified and enduring peace" that protects the enclave's residents.

Nagorno-Karabakh was at the center of two wars between the Caucasus neighbors.

Six weeks of fighting in 2020 ended with a Russian-brokered ceasefire that saw Armenia cede swaths of territory it had controlled for decades.