Azerbaijan on Wednesday accused Armenia of resettling Syrian refugees in a disputed territory the two have been fighting over for decades.
Azerbaijan's UN ambassador said the rival neighbor had started a "very dangerous process with unpredictable consequences" by moving Syrian Armenians into Nagorny Karabakh.
Armenia says it has accepted more than 10,000 ethnic Armenians but has not confirmed they have been moved to Nagorny Karabakh.
Armenian-backed separatists took Nagorny Karabakh from Azerbaijan in a war in the early 1990s that claimed an estimated 30,000 lives. A 1994 ceasefire ended major hostilities, but no peace accord has been reached and clashes regularly erupt. About 20 troops from either side have been killed on their frontier this year.
"We continue to receive the reports testifying to purposeful (Armenian) attempts aimed at encouraging some categories of Syrian refugees to move to other conflict affected areas," Azerbaijan's UN envoy Agshin Mehdiyev told a news conference.
"We have information that they already started it -- settlement of Syrian refugees in occupied territories -- and of course it is a very dangerous process with unpredictable consequences," added Mehdiyev, who is the UN Security Council president for October.
The United Nations recognizes Nagorny Karabakh as part of Azerbaijan. But Azerbaijanis fled after the war and the population is now almost completely ethnic Armenian. In the absence of a peace accord, Azerbaijan and Armenia have rearmed in recent years.
Azerbaijan's Foreign Minister Elmar Mammadyarov raised the Syrian Armenians in a speech to the UN General Assembly last week. The two governments regularly clash over Nagorny Karabakh at the annual UN summit.
"The latest reports on the transfer of Syrian Armenians into the Nagorny-Karabakh region and other seven adjacent occupied districts of Azerbaijan ... provide yet more evidence of Armenia's deliberate policy of annexation of Azerbaijani lands," Mammadyarov said.
Armenia's UN mission did not immediately answer calls about the Azerbaijan claims.
Armenia's Foreign Minister Edward Nalbandyan told the General Assembly last week that his country was "alarmed" by the crisis in Syria.
"The number of refugees Armenia continues to receive already exceeds 10,000, but tens of thousands of Syrian-Armenians still remain in that country."
Tens of thousands of Armenians fled to Syria after the mass killing of Armenians in Ottoman Turkey during World War I.
Nalbandyan criticised Azerbaijan's "destructive" stance on Nagorny-Karabakh.