The Azerbaijani Foreign Ministry on September 22 called a recent visit to Nagorno-Karabakh by three US lawmakers a “provocation” and said it had blacklisted them, RFE/RL reports, citng Russian news agency Interfax.

Azerbaijan’s state-run APA news agency earlier in the week said the ministry had threatened to blacklist the three members of the U.S. House of Representatives. Frank Pallone, David Valadao, and Tulsi Gabbard visited Armenia and made a side trip to Artsakh in Nagorno-Karabakh on September 20.

“Pallone, Valadao, and Gabbard paid an illegal visit to the occupied Azerbaijani territories, thus breaching Azerbaijani law,” Azerbaijani Foreign Ministry spokesman Hikmet Hajiyev told Interfax. “All three are added to the list of undesirable persons in Azerbaijan.”

The legislators’ visit was “a provocation aimed at undermining efforts of the co-chairs of the OSCE Minsk Group, including the United States, in settling the Nagorno-Karabakh conflict,” he told Interfax.

While in Artsakh, the U.S. legislators, who are members of the U.S. Congressional Armenian Caucus, met with Nagorno-Karabakh legislators and visited the Shushi Arts College and a cathedral.

Pallone said the legislators’ goal was to learn and educate the American public about the region.

“We try to learn about the military situation on the border and what measures are being taken to eliminate the consequences of the April war,” Artsakh Press quoted Pallone as saying. He was referring to a sharp uptick in violence in the region that occurred in April.

“One of the goals of our work is to contribute to the activity of the OSCE Minsk Group,and we believe that the people of Artsakh should have the right to self-determination and have security mechanisms,” Artsakh Press quoted Pallone as saying.

Azerbaijan and Armenia have been locked in a conflict over Azerbaijan’s breakaway region of Nagorno-Karabakh for years.

Populated mainly by ethnic Armenians, Nagorno-Karabakh declared independence from Azerbaijan amid a 1988-94 war that claimed an estimated 30,000 lives and displaced hundreds of thousands of people.

Internationally mediated negotiations involving the OSCE’s so-called Minsk Group helped forge a cease-fire in the region, which is not always honored, but have failed to produce a lasting settlement of the conflict.