Armed pirates have kidnapped two Japanese and a Filipino from a tugboat in the Malacca Strait.
The tugboat has been inspected by Malaysian police
The pirates struck on Monday night and seized money and documents from the Japanese-registered boat.
Indonesia sent three navy ships to the area, though officials said the pirates could now be in Malaysian waters.
The attack followed a raid by 35 pirates, armed with rocket launchers, who boarded an Indonesian-owned tanker on Saturday and took two hostages.
Japan's foreign ministry said it had set up a task force to handle the latest incident.
The abducted men include the tugboat's Japanese captain and chief engineer, and a Filipino engineer.
The narrow Malacca Strait between Indonesia and Malaysia is one of the world's busiest shipping lanes and has long been targeted by pirates.
Some 37 acts of piracy were recorded there last year but there has been a sharp fall in reported attacks after December's tsunami in the Indian Ocean.
Some experts said the disaster could have killed many pirates and destroyed their boats, while others believed the presence of international troops in the region deterred attacks.