US Secretary of State Antony Blinken said on Thursday that Azerbaijan and Armenia made progress during three days of negotiations and voiced hope for an accord despite a flare-up in violence.

The adversaries' foreign ministers met at a State Department office in suburban Washington and also went to the White House to see Jake Sullivan, the national security adviser, in the latest US-led mediation.

Closing the talks, Blinken said the two sides had made "further progress" on "the objective of reaching an overall final agreement in the weeks and months ahead" on Nagorno-Karabakh, a breakaway region under effective Armenian control.

"I think there's also a clear understanding on everyone's part that the closer you get to reaching an agreement, in some cases the harder it gets because by definition, the most difficult issues are left for the end," Blinken said.

Blinken saluted the "candor, openness, directness" between Armenian Foreign Minister Ararat Mirzoyan and his Azerbaijani counterpart Jeyhun Bayramov, who traveled to the US capital for the second time in as many months for talks.

The European Union has also been mediating at the level of leaders between the former Soviet republics, stepping into diplomacy where Russia has historically been the chief broker.

With Moscow bogged down by its invasion of Ukraine, Armenia has repeatedly accused Russian peacekeepers of failing to live up to promises to protect ethnic Armenians in line with a Kremlin-brokered ceasefire that ended major fighting in 2020.

While the foreign ministers were visiting in Washington, four Armenian separatist fighters died in renewed Azerbaijani firing, according to the rebels.

Tensions have soared over a months-long blockade of the only land corridor that connects Nagorno-Karabakh to Armenia, with accounts of food and medicine shortages.