Clashes at a Sri Lankan jail have killed 26 people, including seven guards, and wounded more than 100 in the country’s deadliest prison riot in years, officials said.

Victims with cuts and gunshot injuries were rushed to Negombo hospital, north of the capital Colombo after overnight fighting between prisoners from two drug gangs, police said on Monday.

Hospital director Pushpa Gamlath said there were 23 bodies at the state-run facility, as well as more than 100 wounded prisoners and guards from Negombo Prison.

“There are some victims with gunshot injuries, some with cuts and severe bruises,” Gamlath told Agence France-Presse by telephone. “We transferred 18 of the more seriously wounded to the Colombo National hospital.”

Justice minister Harshana Nanayakkara later said three more people had died, raising the toll to 26. He expressed “profound shock and grief”, and said authorities were working to separate the rival gangs in the prison.

“Whether they were inmates, or associated with the underworld, is not relevant to us at this moment,” Nanayakkara told reporters.

“Human beings have died, and there is a deep shock regarding that. This is something that should never have occurred.”

He said fighting began on Sunday evening at the prison, which houses several thousand detainees. As reports of the fighting spread, female inmates in an adjoining section climbed onto a roof and demanded their release. Police said part of the roof collapsed, injuring some of the women.

The government announced it was setting up a three-member team headed by a retired supreme court justice to investigate the riot.

Prison spokesperson Chaminda Gajanayake said no foreign prisoners were affected by the riots, in possible reference to a 22-year-old British woman who has been held at Negombo since her arrest in May last year at the international airport with 46kg of kush, a highly potent form of cannabis.

Large crowds of relatives of prisoners gathered outside Negombo on Monday as the air force deployed drones and a helicopter to monitor the area. Local residents said they heard gunshots and it was reported that the prisoners had grabbed several guns from guards earlier in the day.

Seven guards were killed when they tried to break up the rioting on Monday, a police official told AFP. “The situation got out of hand this morning,” he said.

In December 2020, rioting at another prison in Sri Lanka killed 11 prisoners and wounded 117 during the height of the Covid-19 pandemic, leading the government to release hundreds of prisoners from overcrowded jails.

Official data showed that prisons across Sri Lanka held 41,250 prisoners as of Sunday, about four times their capacity.