MAPUTO, Mozambique — Reports of more than 50 beheadings by Mozambique’s Islamic extremist rebels have raised international alarm over the new level of violence in the country’s north.

The killings mark a bloody turn in the three-year insurgency in Cabo Delgado province, prompting condemnations from the United Nations secretary-general and the presidents of France and Zimbabwe.

In the past two weeks, the extremists have seized nine towns in the Muidumbe district of Cabo Delgado, extending their range from the port of Mocimboa da Praia, which they have held since August, according to reports in local media.

Capturing the town of Muatide, the insurgents established a center on a soccer pitch where they beheaded more than 50 people, according to Pinnacle News, which has correspondents throughout the province.

The rebels abducted 15 boys participating in traditional initiation rites and their five counselors. All 20 were beheaded along with another nine people, Pinnacle reported on Nov. 2. The extremists went on to cut off the heads of 22 more people, Pinnacle reported on Nov. 7.

Mozambique’s government has not confirmed the killings, but Luiz Fernando Lisboa, the Roman Catholic bishop of Pemba, the provincial capital, said this week he had confirmed with a number of sources the report of the killings of the boys at the initiation ceremony. He said it was impossible to say how many had been beheaded in total, according to an interview with German broadcaster Deutsche Welle.

U.N. Secretary-General Antonio Guterres was shocked by the “reported beheading and kidnapping of women and children,” his spokesman said this week. He urged the country’s authorities “to conduct an investigation into these incidents, and to hold those responsible to account.”

French President Emmanuel Macron denounced the violence in a tweet Wednesday. “More than 50 people have been beheaded, women kidnapped, villages looted and then set on fire. Barbarians hijack a religion of peace to sow terror: Islamist terrorism is an international threat that calls for an international response.”

Zimbabwe’s President Emmerson Mnangagwa tweeted that he is “deeply shocked” by the reports of the beheadings. “These acts of barbarity must be stamped out wherever they are found,” he said, adding that Zimbabwe “is ready to assist in any way.”

The extremists’ three-year insurgency in Cabo Delgado has claimed the lives of more than 2,200 people, according to the Armed Conflict Location and Event Data Project. More than 355,000 have been forced to leave their homes, the U.N.’s Office for the Coordination of Humanitarian Affairs said at the end of October.

What started as a few dozen unemployed and disaffected young men inspired by radical Muslim ideology has grown to a force estimated at 3,000, Yussuf Adam, a Mozambican academic who has studied Cabo Delgado for years and visited the province last month, told The Associated Press.

The fact that the rebels have held the Indian Ocean port city of Mocimboa da Praia for three months shows their growing growing strength, he said.

Further south, the city of Pemba and the surrounding areas are inundated with families fleeing the violence. International aid agencies including the World Food Program, the International Committee of the Red Cross and Doctors Without Borders are working to provide emergency food and services to the displaced.

The increasingly assertive extremists launched an attack last month across the border on a town in Tanzania, the Tanzanian government confirmed.

The extremist violence is also threatening the multi-billion dollar investment being made by international companies in Mozambique’s massive deposits of liquified natural gas along the Indian Ocean coastline of Cabo Delgado province.

In its military response to the insurgency, Mozambique’s army has been accused by Amnesty International of several atrocities, including the killings of more than 10 people and burying them in a mass grave. The Mozambican government has also engaged private security companies to help battle the rebels, according to reports in the local media.

Although Mozambique’s President Filipe Nyusi has discussed the problem posed by the extremist rebels with the 15-nation regional group, the Southern African Development Community, he has not officially requested their assistance. Zimbabwe, South Africa and other neighboring countries will not intervene without an official request from Mozambique and agreement by the group, say experts.

Zimbabwe’s ruling party spokesman Patrick Chinamasa in October said although Zimbabwe “has the full capacity to intervene in Mozambique,” any action “must be a collective” initiative of regional countries.

Zimbabwe has sent troops into Mozambique before, sending soldiers to fight the Renamo rebellion in the 1980s and 1990s.

“Militaries in southern Africa are by and large trained for conventional warfare and the situation unfolding in Mozambique may not be amenable to conventional approaches,” said Lawrence Mhandara, an expert on regional security.

“Also, many economies in the region are not performing well and counter-terrorism operations can be expensive financially and in terms of the human cost. There could be a feeling within the region that a military-centric approach to the conflict may not be the best at this moment,” said Mhandara, who teaches in the department of political science at the University of Zimbabwe.

Mutsaka reported from Harare, Zimbabwe.