DHAKA, Bangladesh — At least four people died late Tuesday when members of two criminal factions attacked each other in a sprawling camp for Rohingya refugees, Bangladesh police said.

Twenty other refugees were injured as the two groups opened fire with locally made guns and used sharp weapons at Kutupalong in Cox's Bazar district, said Rafiqul Islam, an additional police superintendent.

Security was heightened in the camps in the district, where more than 700,000 Rohingya refugees from Myanmar have been sheltered by the government, he said.

The official said at least seven Rohingya refugees, including those who died Tuesday, have been killed in clashes to establish dominance in the area over the last few days.

Bangladesh authorities and intelligence officials say some refugees are involved in the illicit drug trade, smuggling, robberies and ransom-seeking.

Earlier Tuesday, the elite security agency Rapid Action Battalion arrested nine refugees suspected of involvement in various criminal activities. They possessed firearms, bullets and sharp weapons, Islam said.

Local media reported that the clash Tuesday began after the arrests when one group accused the other of helping the security agency.

Human rights groups working in the camps acknowledge there are criminals among the refugees.

In January, at least four suspected criminals were killed in a gunfight with police, and in March last year seven others were fatally shot by security officials. They were accused of involvement in drug dealing and human trafficking.

Hundreds of thousands of Rohingya Muslims fled to Bangladesh after the military in Buddhist-majority Myanmar launched a crackdown against them in August 2017 in response to an attack by insurgents.