Bangladesh’s border guard accused the Burmese navy on Wednesday of opening fire on a fishing boat in the Bay of Bengal, underlining tensions over a refugee crisis.

At least four Bangladeshi fisherman were injured, two senior officers with the border guard told Reuters.

“The fishermen, fishing within Bangladesh’s body of water on the Bay of Bengal Cherrha Dwip, were shot by a Burmese navy vessel,” said Mohammad Saiful Absar, contingent commander of Bangladeshi border guard in St Martin. He said the shooting happened on Tuesday morning.

Some 34,000 Rohingya people have fled to Bangladesh from Burma. Violence in Arakan State, home to many Rohingyas, has become the biggest challenge facing Aung San Suu Kyi’s eight-month-old government and has sparked international criticism that the Nobel Peace Prize winner has done too little to help the Muslim minority.

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Bangladesh’s border guard filed a protest letter on Wednesday to its Burmese counterparts, said AbuZar Al Jahid, lieutenant colonel of Bangladeshi border guard in Teknaf.

Zaw Htay, spokesman for Burma’s president’s office, said the government was not aware of the incident or Bangladesh’s protest.

At least 86 people have been killed in recent weeks in a Burmese army crackdown in Arakan State, launched after attacks on police posts near the Bangladesh border in which nine policemen were killed.

Senior Burmese officers cancelled talks with their Bangladeshi counterparts as Burma‘s army was stepping up the anti-insurgency operation in October.

The United Nations’ refugee agency says up to 500,000 undocumented Rohingya live in Bangladesh and it has registered more than 32,000 Rohingya in official camps there.