Border clashes erupted again early Thursday between arch-foes Azerbaijan and Armenia, officials in both countries said, following a pause in fighting amid a flare-up over a decadeslong territorial dispute.

At least 16 people on both sides have been killed since border clashes erupted Sunday between the ex-Soviet republics, which have been locked for decades in a conflict over Armenian occupation of Azerbaijan's Nagorno-Karabakh region.

The territory was seized by ethnic Armenian separatists in a 1990s war that claimed 30,000 lives, though the recent fighting broke out on a northern section of their shared border far from Karabakh.

Azerbaijani forces were "shelling Armenian villages with mortars and howitzers," Armenia's Defense Ministry spokeswoman Sushan Stepanyan said Thursday.

"The fire still continues," she wrote on Facebook.

The Defense Ministry in Baku said in a statement that clashes were ongoing in the north after "Armenians shelled Azerbaijani villages with large-calibre weapons."

The renewed violence erupted after both sides observed a pause in fighting Wednesday.

The clashes that broke out last week have raised fears of a major flare-up in the strategic Caucasus region and prompted calls for an immediate de-escalation from the United States, the European Union and regional power broker Russia.

Internationally mediated peace talks between the two Caucasus nations have so far failed to bring about a solution to their territorial dispute.

Energy-rich Azerbaijan has repeatedly threatened to win control over Karabakh by force after seeing diplomatic efforts to reclaim the territory fail. Armenia has vowed to crush any military offensive.