The White House says President Barack Obama is "deeply concerned" after Azerbaijan's president pardoned a soldier who killed a fellow officer from Armenia.
According to a National Security Council spokesman, Obama felt the decision by Ilham Aliyev to pardon the convicted killer Ramil Safarov was "contrary to ongoing efforts to reduce regional tensions and promote reconciliation.
The spokesman, Tommy Vietor, said Washington was also seeking an explanation from Budapest as to why it decided to extradite Safarov back to Azerbaijan.
Safarov had been serving a life sentence in Hungary for the 2004 axe murder of Gurgen Markarian.
The two were in the Hungarian capital at the time attending a course organized by NATO.
Armenia has already cut diplomatic ties with Hungary and put its troops on "high alert."
Azerbaijan and Armenia fought a war in the 1990s over the disputed territory of Nagorno-Karabakh.
Based on AFP and AP reporting