DAR ES SALAAM (Reuters) - Tanzanian police have arrested 104 suspected militants planning to establish bases in neighboring Mozambique, where scores of people have been killed in Islamist attacks over the last year, a senior official said.

Forty attacks have been carried out since October 2017 in Mozambique’s Cabo Delgado province, an area near the Tanzanian border close to where companies are developing one of the biggest natural gas finds in a decade. More than 100 people have been killed, often by decapitation.

In a press conference on Friday, Inspector General of Police Simon Sirro said security forces had launched operations over the last few months against “criminals” in eastern and southern areas, but that some of them had managed to flee.

“During that operation, some criminals were arrested and some ... died, and a few escaped. Those who escaped are the ones trying to cross the border to Mozambique to establish a base,” he told a news conference.

“After questioning them, they said they were going there to join radical camps,” Sirro added.

Earlier this month, Mozambique put 189 people, including foreigners, on trial on accusations of involvement in Islamist attacks in Cabo Delgado. [L8N1WJ557]

The province is near one of the world’s biggest untapped offshore natural gas fields, and Anadarko Petroleum is seeking to raise $14 billion-$15 billion for a liquefied natural gas project in the region.

In June, President Filipe Nyusi vowed to be relentless and firm in detaining those responsible for the attacks.

Mozambique has no history of Islamist militancy and authorities have been reluctant to ascribe the attacks to Islamists. About 30 percent of Mozambique’s 30 million people are Roman Catholics, while 18 percent are Muslim.

(This story corrects date of press conference to Friday)