YEREVAN, Armenia (AP) — Thousands of people protested in Armenia's capital on Wednesday, demanding the prime minister's resignation after he signed an agreement with Azerbaijan to halt weeks of fighting over Nagorno-Karabakh that calls for Armenian territorial concessions.

The rally organized by opposition parties in Yerevan reportedly drew up to 10,000 people. Some clashed with police, and many were detained and released later in the day.

Demonstrators chanted “Nikol, go away” and “Nikol, the traitor,” referring to Prime Minister Nikol Pashinian, as opposition politicians gathered signatures for an emergency parliament meeting to consider his dismissal.

The unrest was triggered by a Moscow-brokered truce Armenia and Azerbaijan announced early Tuesday after more than six weeks of deadly clashes over Nagorno-Karabakh, a separatist region that lies within Azerbaijan but has been under control of ethnic Armenian forces backed by Armenia since a separatist war there ended in 1994.

The two ex-Soviet nations have been locked in a conflict over the territory for decades. Heavy fighting flared up in late September and has left hundreds, possibly thousands, dead in the biggest escalation in a quarter-century.

Several cease-fires announced over the past six weeks failed to halt the violence, but the current agreement appeared to be holding, with neither side reporting any more fighting since it came into force.

The pact, which is celebrated in Azerbaijan and has angered Armenians, calls for Armenia to turn over control of some areas its holds outside the borders of Nagorno-Karabakh. They include the Lachin region, which the main road leading from Nagorno-Karabakh to Armenia passes through. The agreement calls for the road, the so-called Lachin Corridor, to remain open and be protected by Russian peacekeepers.

The deal also calls for transport links to be established through Armenia that would connect Azerbaijan and its western exclave of Nakhchivan, which is surrounded by Armenia, Iran and Turkey.

A total of 1,960 Russian peacekeepers, some of whom have already arrived in Nagorno-Karabakh, are to be deployed in the region under a five-year mandate to secure the truce.

It came days after Azerbaijan pressed its offensive deeper into Nagorno-Karabakh and took control of the city of Shushi, strategically positioned on heights overlooking the regional capital of Stepanakert.

Nagorno-Karabakh’s separatist leader, Arayik Harutyunyan, acknowledged Tuesday that “had the hostilities continued at the same pace, we would have lost all of Artsakh (an Armenian name for Nagorno-Karabakh) within days.”

Pashinian said in a series of video statements on his Facebook page that it was “extremely painful for me personally and for our people,” calling the situation a “catastrophe." On Wednesday, he said he signed the agreement to avoid “a full collapse” of the region and deaths of thousands of troops.

Armenian opposition politicians on Wednesday called the agreement “treacherous" and demanded that Pashinian step down.

“We need to save Armenia and Artsakh from Pashinian,” Ishkhan Saghatelyan, member of the Armenian Revolutionary Federation — Dashnaktsutyun political party, said at the rally in Yerevan.

Opposition lawmakers on Wednesday evening announced that they have gathered enough signatures to call an emergency parliament session to consider ousting Pashinian, scheduled to start at 16:00 GMT.

It remains unclear whether the opposition will be able to follow through with the ouster, as Pashinian's My Step faction holds the overwhelming majority — 88 seats out of 132 — in the country's parliament.

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Associated Press writer Daria Litvinova in Moscow contributed to this report.