Somali pirates hijacked a ship en route from Dubai yesterday and Spain said it had sent a naval frigate after the seizure of a Spanish tuna fishing boat with 26 people aboard off Somalia.

A surge in hijackings for ransom off lawless Somalia have made it one of the world's most dangerous shipping zones.

The Dubai-flagged Al-Khaleej was carrying food for sale in Somalia when it was held up seven kilometres off the northeastern Somali port of Bosasso, authorities there said.

"If these pirates have now gone ahead to hijack vessels bringing us food, this will badly affect activities at our port. We need to do something about them," said Abdisamad Yusuf Abwaan, commerce and industry minister for the semi-autonomous northeast Puntland region.

Suspected Somali pirates also fired on a Japanese-flagged chemical carrier off Yemen yesterday. And Madrid said it had sent a naval frigate to help rescue the Spanish tuna fishing boat, which was attacked on Sunday.

The attackers appear undeterred by French troops' arrest in the desert last week of six Somali pirates who seized a French luxury yacht and held its crew hostage for a week. They were flown to France for questioning.

The Spanish Foreign Ministry said 13 of the people on board the tuna fishing boat, called Playa de Bakio, were Spanish, and added it was in touch with governments with military presence in the area to help find the vessel. Media reported on Sunday that the boat was attacked with grenade launchers about 250 miles from the coast and boarded by armed men. They said the boat was heading towards the Somali coast.

Spanish national radio quoted the captain of the boat as saying everybody on board was well. A man who said he was one of the captors said in broken English that the pirates were Somalis and wanted money.

Somali authorities said the hijackers were taking the Spanish boat to Garad port, in south Puntland.

Somalia has been without an effective central government since the 1991 toppling of a military dictator, allowing anarchy and violence to flourish.

Kidnapping and piracy are lucrative businesses and most Somalis treat their captives well in anticipation of a ransom.

A Kenyan-based regional maritime group, the Seafarers' Assistance Programme, said suspected Somali pirates fired at a Japanese-flagged chemical carrier off Yemen yesterday, causing minor damage but no injuries. It added that suspected Somali pirates fired on a Japanese-flagged chemical carrier off Yemen on Monday.

"The Japan-flagged 264,457 dwt Takayama, bound from South Korea for Saudi Arabia in ballast, was hit by what is thought to have been a rocket-propelled grenade in the Gulf of Aden at 0440 hrs local time this morning," it said in a statement.

"The vessel reportedly suffered minor damage to the hull close to the stern, resulting in a minor spill of fuel oil."

The Kenyan-based seafarers' programme added that there were no injuries to the 23 crew and the ship was able to proceed.