Philippines militant group Abu Sayyaf has released 10 Indonesian seafarers seized from a tug last month.

The lead Indonesian negotiator, retired army general Kivlan Zein, said no ransom was paid.

The terrorist organisation wanted $1m for the men taken from the 2015-built Brahma 12 on 26 March.

The ship was pulling a barge carrying coal.

"The release was conducted without paying a ransom, based on negotiations and cooperation between the TNI [Indonesian military] and the Philippine military," Kivlan said on Monday, according to Antara news agency.

The tug is operated by Patria Maritime Lines, part of United Tractors.

Four crew from another Indonesia tug remain in captivity in the Philippines.