"About 12 pirates armed with guns attacked the tug and barge and kidnapped two crew members as the vessel was en route to Singapore."
The source said the rest of the crew and the boat were not seized.
The attack occurred in the north of the Malacca Strait, a strategic waterway bordered by Malaysia, Indonesia and Singapore, the source said.
Noel Choong, head of the International Maritime Bureau (IMB) piracy reporting centre in Kuala Lumpur, confirmed the incident had taken place but declined to elaborate due to concerns over the safety of the kidnapped crew.
"The IMB is concerned about this recent kidnapping. We hope this is not a start of more attacks to come. We hope regional authorities will beef up patrols," he said.
"We urge seafarers to be alert when plying the Malacca Strait."