“If Armenian forces continue targeting settlements and civilians, Armenia will bear the responsibility for the actions of Azerbaijani army, which will ensure the safety of civilians,” Foreign Ministry spokesman Hikmet Hajiyev said in a statement.
He said Armenia continued to shell Azerbaijani positions “intensively” despite Azerbaijan declaring a cease-fire on Sunday.
The U.S. reiterated that it condemned in the strongest terms the current violence in occupied Karabakh.
"We strongly support the co-chair's [Minsk Group] efforts to mediate a fair and just resolution to Nagorno-Karabakh that is based on the principles of international law, the U.N. Charter and the Helsinki Final Act," State Department spokesman Mark Toner said.
"Particularly principles of non-use of force, territorial integrity and self-determination."
Meanwhile, Secretary of State John Kerry and his Russian counterpart Sergey Lavrov spoke via telephone Monday to discuss efforts for "an immediate end of the violence" and to resume talks under the auspices of the OSCE's Minsk Group.
The international organization co-chaired by Russia, the U.S. and France, aims to find a peaceful resolution to the conflict between Azerbaijan and Armenia.
Though speaking to Lavrov, Kerry has not spoken to his Azerbaijani nor Armenian counterparts, according to Toner.
But a tweet by U.S. Vice President shows that U.S. authorities are currently in conversation with Azerbaijan and Armenia.
"As I told Presidents Aliyev & Sargsyan, comprehensive settlement in #NagornoKarabakh is critical for their stability, security, prosperity," Joe Biden said on his Twitter account.
The U.S, reaction comes after 12 Azerbaijani troops and more than 100 Armenian soldiers were killed during weekend fighting over Karabakh, which was seized by ethnic Armenian separatists in the early 1990s.
In a separate statement, the Azerbaijani Defense Ministry said an Armenian command post and three tanks had been destroyed.