Indonesian authorities have been accused of assaulting a number of Sri Lankans who are aboard a boat in Indonesia's Merak port.

Sanjeev Kuhendrarajah, also known as 'Alex', says Indonesian police, military and immigration officials attacked him and five other men.

The 250 Tamil asylum seekers, who were trying to reach Australia, have refused to leave the boat since the Indonesian navy intercepted it in October.

Alex says he has been deliberately targeted since being accused of people smuggling. He says he was verbally abused and physically assaulted during the encounter.

"He just grabbed me right away and once the navy colonel grabbed me then all the other officers that were there in that tent, they starting grabbing me, and ripped my shirt apart, they put me on the floor and starting stomping on me, and they punched me in the face," he said.

"And, I'm a brown skin I don't get bruises, but the other boys that were standing there, they did try to stop these people and when they did try to stop them they were getting pushed around too."