MANILA (Reuters) - Philippine militants took two crew captive from a cargo ship on Thursday, only hours after soldiers rescued two Malaysians held for about eight months on a southern island, officials said.

The vessel was on its way to General Santos City on the southern island of Mindanao from the central Philippines when gunmen in three speed boats intercepted it, a coast guard commander said.

“Two Filipino crew, the ship’s captain and chief engineer, were taken captive,” Lieutenant-Commander Alvin Dagalea told reporters.

“The reports are still sketchy, but we have reasons to believe the Abu Sayyaf are behind the attack.”

In the nearby Sulu archipelago, troops rescued two Malaysian captives in waters off Pata island, said Major General Carlito Galvez Jr., commander of the Western Mindanao Command.

The two, who were among five Malaysian tugboat crew seized by militants in July last year off the Malaysian state of Sabah, were weak and “in sickly state” when rescued, Galvez said.

The small but violent Islamist Abu Sayyaf, based in the south of the mainly Roman Catholic Philippines, is known for kidnappings, beheadings, bombings and extortion. It is widely believed that no captives are released by the group without ransom being paid.

This month, President Rodrigo Duterte pleaded for help from mayors in Muslim parts of the south to deal with the militants and threatened to impose martial law there if the problem was not tackled.

Defence Secretary Delfin Lorenzana has described Abu Sayyaf’s kidnappings as a national embarrassment, saying the number of hostages had increased to 31 from 18 captives when Duterte came to power on June 30.