International negotiators say Azerbaijan's pardoning of a military officer who murdered an Armenian officer has harmed attempts to establish peace between the countries.
Azerbaijan in turn strongly defended the move, saying the pardon of Ramil Safarov is a consequence of Armenian occupation of a part of Azerbaijan.
The Nagorno-Karabakh region of Azerbaijan and some adjacent territory has been under the control of Armenian troops and local ethnic Armenian forces since a 1994 cease-fire ended a six-year war that killed an estimated 30,000 people and drove about 1 million from their homes.
Negotiators from Russia, the United States and France under the auspices of the Organization for Security and Cooperation in Europe have led efforts since then to find a resolution to the conflict, but with little visible result.
The tensions rose sharply last week after Hungary repatriated Safarov, who had been sentenced to life imprisonment for the 2004 axe murder of Armenian Lt. Gurgen Makarian while both were in Hungary on a NATO language-training course.
Hungary said Azerbaijan promised that Safarov would serve his sentence in a local prison, but he received a presidential pardon hours after returning and later was promoted from lieutenant to major.
An outraged Armenian President Serge Sarkisian broke diplomatic relations with Hungary and said Armenia was willing to resume fighting against Azerbaijan.
Reigniting the frozen conflict would be of serious concern to Russia, which borders Azerbaijan and has a military base in Armenia, as well as the West. A major pipeline through Azerbaijan transports Caspian Sea oil to Turkey and both countries have potential strategic importance because they border Iran.
The co-chairs of the "Minsk Group," the troika negotiating on Nagorno-Karabakh, met in Paris with the Armenian foreign minister on Sunday and his Azerbaijani counterpart on Monday.
The co-chairs "expressed their deep concern and regret for the damage the pardon and any attempts to glorify the crime have done to the peace process and trust between the sides," an OSCE statement said.
Azerbaijani Foreign Minister Elmar Mamedyarov also spoke by telephone with U.S. Deputy Secretary of State William Burns on Monday, ministry spokesman Elman Abdullayev said.
Mamedyarov "underlined that the question of Ramil Safarov must not be looked at outside the context of the fact of the occupation, because it is a consequence of this Armenian aggression," Abdullayev said.
Armenian Foreign Minister Edvard Nalbandian in turn said the "international society cannot tolerate the continuation of Azerbaijan's adventurist policy under the cover of the negotiations process."
Separately from the OSCE statement, Russia's Foreign Ministry condemned both Hungary's release of Safarov and Azerbaijan's pardon of him.
"We believe that these actions of Azerbaijani as well as Hungarian authorities contradict internationally brokered efforts, of the OSCE's Minsk group in particular, to ease tensions in the region," the ministry said.
The White House also criticized the decision to free Safarov.
During his trial in Budapest, Safarov claimed that the Nagorno-Karabakh conflict was at the root of his actions and that he killed Markarian while the victim was sleeping after the Armenian repeatedly provoked and ridiculed him.
Aida Sultanova in Baku, Azerbaijan, and Avet Demourian in Yerevan, Armenia, contributed to this report