Malaysian authorities have arrested four Indonesian pirates who tried to hijack a tugboat and barge off Borneo island in the first such attack there this year, an official said on Saturday. The machete-wielding men boarded the Malaysian vessel off Sarawak state Thursday with most of the crew of ten managing to lock themselves inside the tugboat and raise the alarm, Abim Sungom of the Malaysian Maritime Enforcement Agency said. Authorities captured four suspects from the barge loaded with containers while several others escaped. The four were in custody and are being investigated for robbery, Abim said, adding the incident was the first attack off Sarawak this year. None of the crew, comprising four Malaysians, four Indians and two Indonesians was injured but some valuables, including mobile phones and cash, were stolen, he added. The vessel was heading from peninsular Malaysia to Borneo island, which is occupied by Malaysia, Indonesia and Brunei. Pirate attacks in Malaysian waters have decreased in recent years following beefed up patrols and co-operation with neighbouring countries to secure waterways.