KUALA LUMPUR, Malaysia — Pirates hijacked a Philippines chemical tanker with 23 crew near Somalia, bringing the total number of attacks in waters off the impoverished African country this year to 83, a maritime official said Tuesday.

The tanker was heading to Asia when it was seized Monday in the Gulf of Aden by pirates armed with automatic weapons and rocket-propelled grenades, said Noel Choong, who heads the International Maritime Bureau's piracy reporting centre in Kuala Lumpur.

In Manila, Foreign Ministry spokesman Claro Cristobal said the Philippine Embassy in Nairobi and the ship's operator identified the chemical tanker as the MT Stolt Strength.

All 23 seamen on board are Filipino and are "reportedly unharmed," he said, adding that Philippine authorities are co-ordinating with the ship's operator to secure the early safe release of the vessel and crew.

Choong said there was an attempted attack the same day on a refrigerated cargo ship in eastern Somalia, but the vessel managed to escape with evasive manoeuvring. The ship flies a Saudi flag but is operated out of Britain.

Separately, the Indian navy said its marine commandos operating from a warship prevented pirates from hijacking an Indian merchant vessel in the Gulf of Aden on Tuesday.

The vessel raised the alarm over the radio after pirates attempted to seize it, and an Indian warship patrolling nearby responded, a navy statement said.

A helicopter carrying the commandos intercepted the pirates' vessel and prevented it from boarding the Indian ship -- MV Jag Arnav owned by India's Great Eastern Shipping Ltd.

"This timely and successful intervention led to the pirates aborting their attempt," the navy statement said, adding the merchant ship was then escorted to safety.