A major Japanese oil tanker was damaged and then chased by heavily armed pirates off the coasts of Somalia and Yemen on Monday but no one was injured, officials and crew members said.
It came a day after a Spanish tuna fishing boat carrying a crew of 26 was seized by pirates in waters off Somalia, which has not had an effective central government for more than 17 years.
The area is plagued by insecurity and considered to be among the most dangerous waterways for shipping in the world.
The 150,000-tonne tanker Takayama, with a crew of 23, sustained damage but was able to sail on its own power after the attack at about 4:40 am local time (0140 GMT), its owner and operator Nippon Yusen Kaisha (NYK Line) said here.
"We heard one big boom at first and then we were chased by the group for about an hour," a crew member told Japanese public broadcaster NHK. "We were attacked on the left and the right sides of the ship at least four times."
The attack occurred in international waters some 440 kilometres (275 miles) east of the Yemeni port of Aden, Japanese officials said.
"We have received information that the tanker was attacked by a small pirate ship with weapons like rocket launchers," chief Japanese government spokesman Nobutaka Machimura told reporters.
Nippon Yusen said one unidentified boat was involved in the attack, while a Japan Coast Guard official said the number of vessels operated by the pirates had yet to be confirmed.
The tanker's crew included 16 Filipinos and seven Japanese, the shipping company said in a statement.
Noel Choong, head of the Malaysia-based International Maritime Bureau's Piracy Reporting Centre, told that "pirates on five speed boats" attacked the tanker.
Choong said the pirates could have used rocket-propelled grenades and machine gun fire. "But the tanker increased speed and managed to prevent the pirates from boarding and taking control of the oil tanker."
The tanker was on its way to the Saudi port of Yanbu in the Red Sea after unloading oil at the South Korean port of Ulsan when the attack happened, the company statement said.
A Yemeni maritime source told the tanker diverted to Aden for repairs caused during the incident.
Choong said there had been nine attacks in the Gulf of Aden since February.
The International Maritime Bureau has urged ships plying the gulf to maintain strict 24-hour anti-piracy vigilance against small suspicious boats coming towards them.
In early April, a luxury French cruise yacht with around 30 crew was hijacked off the coast of Somalia.
The hostages were released when a ransom, believed to be around two million dollars (1.3 million euros), was paid.