MOSCOW (Reuters) -Azerbaijan captured six Armenian servicemen in the early hours of Thursday morning, the defence ministries of both countries said, the latest twist in a simmering border dispute.
The Azeri defence ministry accused the Armenian soldiers of trying to cross into Azeri territory. Armenia's defence ministry said its soldiers had been carrying out engineering work in the border area of its eastern Gegharkunik region, which neighbours Azerbaijan.
"Necessary measures are being taken to return the captured servicemen," Armenia's defence ministry said.
The United States said it was concerned by the border incidents between Armenia and Azerbaijan, including the detention of several Armenian soldiers, urging both sides to "urgently and peacefully" resolve the issue.
In a statement, the U.S. State Department said it considered any movements along the non-demarcated areas of Azerbaijan and Armenia border to be "provocative and unnecessary".
In separate comments, Armenia's acting Prime Minister Nikol Pashinyan called for international observers from Russia or other countries to be deployed to a portion of Armenia's border with Azerbaijan, where he said the atmosphere was tense.
Pashinyan also directed his proposal at the Azerbaijan leadership, Russian news agencies quoted him as saying.
"Let's agree that the military units from both sides rapidly move away from the border and return to their permanent bases, and station international observers from Russia or other countries in the OSCE Minsk Group."
The U.S. State Department also urged both sides to return as soon as possible to substantive negotiations under the auspices of the OSCE Minsk Group Co-Chairs to achieve a long-term political settlement to the Nagorno-Karabakh conflict.
Armenia earlier this month accused Azerbaijan of sending troops across the border, highlighting the fragility of a Russian-brokered ceasefire that halted six weeks of fighting between ethnic Armenian forces and the Azeri army last year.
That conflict saw Baku drive ethnic Armenian forces out of swathes of territory they had controlled since the 1990s in and around the Nagorno-Karabakh region.
Azerbaijan on Tuesday denied accusations by Armenia that it had fired across the border at Armenian positions, in a shootout in which Armenia said one of its soldiers had been killed.
(Reporting by Anton Kolodyazhnyy, Alexander Marrow and Gabrielle Tétrault-Farber; additional reporting by Humeyra Pamuk in Washington; Editing by Andrew Osborn, Toby Chopra and Grant McCool)