Separatists said that Azerbaijan pounded the mountainous territory with artillery, jets and drones on Tuesday -- one day after aid was allowed in through the sole road link from Armenia to Nagorno-Karabakh.

France called for the Security Council to meet on the crisis, which comes as leaders gather in New York for the annual General Assembly. Albania, which holds the rotating Security Council presidency, announced a session would take place Thursday.

This operation is "illegal, unjustifiable and unacceptable," French Foreign Minister Catherine Colonna told reporters.

"I would like to emphasize that we hold Azerbaijan responsible for the fate of Armenians of Nagorno-Karabakh," Colonna said.

German Chancellor Olaf Scholz voiced alarm during his speech to the General Assembly, saying, "The renewed military activities lead to a dead end. They need to end."

US Secretary of State Antony Blinken, also in New York for the meetings, spoke by telephone with the leaders of both Armenia and Azerbaijan, with French President Emmanuel Macron also speaking to Armenian Prime Minister Nikol Pashinyan.

Blinken, in a call with Azerbaijan's President Ilham Aliyev, urged him "to cease military actions in Nagorno-Karabakh immediately and deescalate the situation," State Department spokesman Matthew Miller said.

At least 29 people have died in the offensive, which comes three years after an earlier war in which Azerbaijan won back broad areas.

Russia joins calls for calm 

France is looking for unanimous condemnation of Azerbaijan. Unlike on many issues, Russia has largely joined Western powers in supporting calls for calm, even as it voices alarm over greater European and US efforts between the former Soviet republics.

Russia after 2020 sent peacekeepers but Armenia had already accused Moscow of failing to live up to its obligations as it is distracted by the Ukraine war.

Protesters rallied in Yerevan on Tuesday outside the Russian embassy in anger that Russia did not prevent the offensive by Azerbaijan.

The United States was also in touch with Turkey, which has cultural ties with Azerbaijan. Turkish President Recep Tayyip Erdogan, who was in New York, voiced support for the offensive in Nagorno-Karabakh, which is internationally recognized as part of Azerbaijan.

A senior US official voiced frustration that the violence came just one day after the world welcomed the aid delivery through the Lachin corridor, which had been blocked for months.

"We had actually good news yesterday," the official said on condition of anonymity.

"We were hopeful that we were going to be able to adapt to the longer-term issues," the official said, "so that makes this incident overnight particularly egregious and particularly dangerous."

France and the United States both have large and active Armenian diasporas. France has been especially supportive of Armenia, with Azerbaijan recently protesting after French mayors tried to force aid into Karabakh.

Blinken has fashioned himself as a neutral mediator and has led three rounds of peace talks with the Armenian and Azerbaijani foreign ministers.

In Washington, Senator Bob Menendez, who heads the Senate Foreign Relations Committee, accused Azerbaijan of pursuing a campaign of "ethnic cleansing" against Christian Armenia.

The Democrat said he would introduce legislation in the coming days to punish Aliyev.

"We must provide immediate support to Nagorno-Karabakh and work with international partners to bring pressure on Aliyev to stop his ruthless campaign," Menendez said.

Also calling for action was Argentine President Alberto Fernandez who in his speech to the General Assembly called on the two sides to show "sanity."

"The international community cannot remain passive," he said.