Nearly 3,000 migrants have swum to shore or been rescued off Indonesia, Malaysia and Thailand over the past week, around half of whom have arrived in Indonesia's western province of Aceh.
The three nations have sparked outrage by turning away some overloaded vessels, and thousands of migrants are still believed to be stranded at sea after a Thai crackdown disrupted long-established people-smuggling and -trafficking routes.
Yesterday, the Indonesian navy stopped a boat from entering its waters after the vessel was spotted heading across the Malacca Strait from the direction of Malaysia, Indonesian armed forces spokesman Fuad Basya told AFP.
After radio communication with the boat, it turned back from Indonesia, he said, adding it was not physically pushed back. Basya said it was believed the boat was carrying more migrants, although he was not sure how many.
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A week ago the navy stopped a boat carrying hundreds of migrants from entering Indonesia, and the military insists it will only help vessels in distress.
Basya said four warships and one plane were now patrolling off Aceh's coast to stop migrant boats from entering, up from one warship and a plane around a week ago.
"The boats are forbidden from entering Indonesia," he said.
On Friday fishermen rescued hundreds of migrants from a sinking boat off Aceh, on the huge island of Sumatra. Fighting had erupted on board between the Rohingya, a persecuted Muslim minority from Myanmar and the Bangladeshis, and many leapt or were thrown overboard.