YEREVAN, Armenia — Azerbaijani forces pushed deeper into Nagorno-Karabakh on Friday as top diplomats from Armenia and Azerbaijan were scheduled to attend talks in Geneva intended to help broker an end to more than a month of heavy fighting over the separatist territory.

Intense clashes were going on in the south of Nagorno-Karabakh, Armenia’s Defense Ministry said. The Azerbaijani military reported that areas in the Terter and Gubadli regions of Azerbaijan came under Armenian shelling.

On Thursday, Nagorno-Karabakh’s separatist leader said Azerbaijani troops had advanced to within 3 miles of a strategically located town just south of the region’s capital, Stepanakert. He urged residents to mobilize all their resources to fend off the attack on Shushi, a town which sits on the main road linking Nagorno-Karabakh with Armenia.

“The one who controls Shushi controls Nagorno-Karabakh,” Arayik Harutyunyan said in a video address from the town’s cathedral, which was severely damaged by Azerbaijani shelling this month.

Harutyunyan’s statements marked a somber acknowledgment of Azerbaijani gains in the fighting over Nagorno-Karabakh that started on Sept. 27. The latest outburst of hostilities has left hundreds and possibly thousands of people dead, marking the largest escalation in the region in more than a quarter-century.

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. In that war, Armenian forces also seized several regions of Azerbaijan around Nagorno-Karabakh, creating a buffer zone around the territory.

Azerbaijani troops, which have relied on strike drones and long-range rocket systems supplied by Turkey, have reclaimed control of some of those regions in the latest fighting and forged into Nagorno-Karabakh from the south.

A U.S.-brokered truce frayed immediately after it took effect Monday, just like two previous cease-fires negotiated by Russia. The warring sides have repeatedly blamed each other for violations.

According to Nagorno-Karabakh officials, 1,166 of their troops and 39 civilians have been killed. Azerbaijani authorities haven’t disclosed their military losses, but say the fighting has killed at least 90 civilians and wounded 392.

But Russian President Vladimir Putin said last week that, according to Moscow’s information, the actual death toll was significantly higher and nearing 5,000.

Russia, the United States and France have co-chaired the so-called Minsk Group set up by the Organization for Security and Cooperation in Europe to mediate in the conflict, but they have failed to score any progress. Top diplomats from the three countries were scheduled to meet with the foreign ministers of Armenia and Azerbaijan in Geneva on Friday for talks on ending hostilities, but there was no hope of a quick breakthrough.

Azerbaijani President Ilham Aliyev has insisted that Azerbaijan has the right to reclaim its territory by force after three decades of international mediation have produced no result. He said that Armenia must pledge to withdraw from Nagorno-Karabakh as a condition for a lasting truce.

Associated Press writers Vladimir Isachenkov in Moscow and Aida Sultanova in London contributed to this report.