Two sailors aboard a  Singapore-managed boat have been kidnapped by pirates in the Malacca Strait, sources say.

The nationality of the sailors was not known, and it was not clear whether negotiations to secure their release had begun.

"A Singapore-managed tug and barge was attacked in the Malacca Strait on February 19 in the afternoon," a maritime source familiar with the incident told the AFP news agency on Friday.

"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."