Armenia and Azerbaijan on Monday accused each other of attacks over the separatist territory of Nagorno-Karabakh despite a cease-fire deal brokered by Russia to try to end the worst outbreak of hostilities in the region in decades.

The cease-fire came into effect Saturday, but was immediately challenged by mutual claims of violations that persisted since then.

Armenian Defense Ministry spokeswoman Shushan Stepanian said Azerbaijani forces were “intensively shelling the southern front” of the conflict zone on Monday morning. Nagorno-Karabakh officials said Azerbaijan directed a “large number of forces” to the area of Hadrut, a town in the south of the region, and reported “large-scale hostilities” there.

Azerbaijan’s Defense Ministry called those accusations “disinformation” and insisted that Azerbaijan was observing the cease-fire. The ministry in turn accused Armenian forces of shelling the Goranboy, Terter and Agdam regions of Azerbaijan.

Armenian military officials also said that Nagorno-Karabakh forces shot down an Azerbaijani Su-25 warplane, a claim that Azerbaijan denied.

The recent fighting between Azerbaijani and Armenian forces started Sept. 27 and has left hundreds of people dead in the biggest escalation of the decades-old conflict over Nagorno-Karabakh since a separatist war there ended in 1994. The region lies in Azerbaijan but has been under control of ethnic Armenian forces backed by Armenia.

The foreign ministers of Armenia and Azerbaijan signed a truce in Moscow after Russian President Vladimir Putin had brokered it in a series of calls with Azerbaijani President Ilham Aliyev and Armenian Prime Minister Nikol Pashinian.

The cease-fire took effect at noon Saturday following talks in Moscow sponsored by Russian Foreign Minister Sergey Lavrov. The deal stipulated that the cease-fire should pave the way for talks on settling the conflict.

If the truce holds, it would mark a major diplomatic coup for Russia, which has a security pact with Armenia but has also cultivated warm ties with Azerbaijan. But so far the agreement “is not being adhered to in full, and hostilities continue,” Lavrov said Monday at a meeting with his Armenian counterpart.

Both Armenia and Azerbaijan reiterated their commitment to the deal and accused each other of violating it.

Turkey, which has publicly sided with Azerbaijan in the conflict, also accused Armenia of violating the truce.

“They have no respect for international law or for humanitarian values,” Turkish Defense Minister Hulusi Akar said. “They have ruthlessly attacked Ganja and other civilian settlements and continue to do so. This amounts to the breach of the cease-fire.”

U.N. Secretary-General Antonio Guterres was “very disappointed” at the reported cease-fire violations, which he called “unacceptable,” according to U.N. spokesman Stephane Dujarric.

“The secretary-general condemns any targeting and attacks against civilian-populated areas anywhere and regrets the loss of life and injuries,” he said.

“We call on all parties again to fulfill their agreements to a humanitarian cease-fire and other commitments announced in Moscow” and remain ready to respond to any humanitarian needs if requested, Dujarric said.

Residents of Nagorno-Karabakh’s capital of Stepanakert, which came under intense shelling last week, told The Associated Press on Monday it didn’t feel like a truce to them.

“We do not feel the cease-fire at all. We do not get out from here to our flats,” said Larisa Azeryan, who has been staying in a shelter in the basement of an apartment building. “We all stay here, we eat here, sleep here. The whole day is spent here in the basement.”

Lavrov urged both sides in the conflict to “rigorously observe” the agreements reached in Moscow and warned against delaying “the political negotiation process”. The minister said he believed that the long cease-fire talks on Friday night were not “in vain,” and that it was possible to change “the situation on the ground” in the nearest future.