YEREVAN (Azatutyun.am)—The Armenian and Azerbaijani foreign ministers made further progress toward a bilateral peace treaty but still disagree on some of its key terms, official Yerevan said on Thursday night after they concluded a new round of U.S.-mediated negotiations.

Foreign Minister Ararat Mirzoyan and his Azerbaijani counterpart Jeyhun Bayramov met outside Washington for three consecutive days. They also held trilateral meetings with U.S. Secretary of State Antony Blinken and National Security Adviser Jake Sullivan.

“The Ministers and their teams continued progress on the draft bilateral ‘Agreement on Peace and Establishment of Interstate Relations,’” read a statement released by the Armenian Foreign Ministry.

“They reached an agreement on additional articles and advanced mutual understanding of the draft agreement, meanwhile acknowledging that the positions on some key issues require further work,” it said, adding that Mirzoyan and Bayramov pledged to “continue their negotiations.”

The statement did not disclose those articles or the remaining sticking points. It reflected Blinken’s comments made during the final session of the three-day talks.

The top U.S. diplomat also said that “there remains hard work to be done to try to reach a final agreement.”

“I think there is also a clear understanding on everyone’s part that the closer you get to reaching agreement, in some cases the harder it gets by definition. The most difficult issues are left for the end,” added Blinken.

The two sides were understood to disagree before the latest talks on practical modalities of delimiting the Armenian-Azerbaijani border and a dialogue between Baku and Nagorno-Karabakh’s leadership as well as international safeguards against non-compliance with the treaty.

Yerevan has been pressing for an “international mechanism” for such a dialogue, saying that it is essential for protecting “the rights and security” of Karabakh’s ethnic Armenian population. Bayramov made clear late last week that Baku will not agree to any special security arrangements for the Karabakh Armenians.