Armenia and Azerbaijan on Monday accused each other of violating the new cease-fire announced the day before in a bid to halt the fighting over the separatist region of Nagorno-Karabakh that has killed hundreds, and possibly thousands, in just four weeks.

The truce that took effect Monday morning was agreed upon on Sunday after talks facilitated by the United States. It was a third attempt to establish a lasting cease-fire in the flare-up of a decades-old conflict. Two previous Russia-brokered cease-fires, including one last weekend, frayed immediately after taking force, with both sides blaming each other for violations.

The new cease-fire was also challenged quickly by accusations from both sides. Azerbaijani Defense Ministry alleged that Armenian forces fired at Azerbaijani settlements and the positions of the Azerbaijani army “along the entire front, as well as on the Armenia-Azerbaijan state border" using various small arms, mortars and howitzers.

Citizens inspect a car destroyed during a shelling by Azerbaijan's artillery during a military conflict in Stepanakert, the separatist region of Nagorno-Karabakh, Friday, Oct. 23, 2020. Heavy fighting raged Friday over Nagorno-Karabakh even as top diplomats from Armenia and Azerbaijan visited Washington for negotiations on settling the neighboring countries' decades-long conflict. (AP Photo)

Citizens inspect a car destroyed during a shelling by Azerbaijan's artillery during a military conflict in Stepanakert, the separatist region of Nagorno-Karabakh, Friday, Oct. 23, 2020. Heavy fighting raged Friday over Nagorno-Karabakh even as top diplomats from Armenia and Azerbaijan visited Washington for negotiations on settling the neighboring countries' decades-long conflict. (AP Photo)

Armenian military officials rejected the accusations and in turn accused Azerbaijani forces of shelling the northeastern area of Nagorno-Karabakh and other areas.

Nagorno-Karabakh lies within Azerbaijan but has been under the control of ethnic Armenian forces backed by Armenia since a war there ended in 1994. The latest fighting that began Sept. 27 has involved heavy artillery, rockets and drones, killing hundreds in the largest escalation of hostilities over the separatist region in more than a quarter-century.

According to Nagorno-Karabakh officials, 974 of their troops and 37 civilians have been killed in the clashes so far. Azerbaijani authorities haven’t disclosed their military losses, but say the fighting has killed 65 civilians and wounded 300.

In this photo provided by the Armenian Prime Minister Press Service via PAN Photo, Armenian Prime Minister Nikol Pashinyan speaks to a wounded serviceman as he visits a military hospital in Yerevan, Armenia, Friday, Oct. 23, 2020. Heavy fighting is raging over Nagorno-Karabakh even as top diplomats from Armenia and Azerbaijan have traveled to Washington for negotiations on settling the neighboring countries’ decades-long conflict. (Tigran Mehrabyan, Armenian Prime Minister Press ServicePAN Photo via AP)

In this photo provided by the Armenian Prime Minister Press Service via PAN Photo, Armenian Prime Minister Nikol Pashinyan speaks to a wounded serviceman as he visits a military hospital in Yerevan, Armenia, Friday, Oct. 23, 2020. Heavy fighting is raging over Nagorno-Karabakh even as top diplomats from Armenia and Azerbaijan have traveled to Washington for negotiations on settling the neighboring countries’ decades-long conflict. (Tigran Mehrabyan, Armenian Prime Minister Press ServicePAN Photo via AP)

Russian President Vladimir Putin said last week that according to Moscow’s information, the death toll from the fighting was nearing 5,000, significantly higher than what both sides report.

The new cease-fire deal brokered by the U.S. came out of “intensive negotiations” Washington facilitated over the weekend among the foreign ministers of Armenia and Azerbaijan and co-chairs of the Minsk Group, set up by the Organization for Security and Cooperation in Europe in the 1990s to mediate the conflict.

Daria Litvinova in Moscow and Aida Sultanova in London contributed to this report.

Men sit in a bomb shelter during shelling by Azerbaijan's artillery during a military conflict in Stepanakert, the separatist region of Nagorno-Karabakh, Friday, Oct. 23, 2020. Heavy fighting raged Friday over Nagorno-Karabakh even as top diplomats from Armenia and Azerbaijan visited Washington for negotiations on settling the neighboring countries' decades-long conflict. (AP Photo)

Men sit in a bomb shelter during shelling by Azerbaijan's artillery during a military conflict in Stepanakert, the separatist region of Nagorno-Karabakh, Friday, Oct. 23, 2020. Heavy fighting raged Friday over Nagorno-Karabakh even as top diplomats from Armenia and Azerbaijan visited Washington for negotiations on settling the neighboring countries' decades-long conflict. (AP Photo)