(Adds Spanish government action)

By Abdiqani Hassan

BOSASSO, Somalia, April 22 (Reuters) - Somali troops stormed a Dubai-flagged ship on Tuesday that had been hijacked off the Horn of Africa nation, releasing its crew and arresting seven pirates, authorities said.

They pledged to do the same to rescue a Spanish ship held by pirates since the weekend.

"Our troops stormed on to the Al-Khaleej and engaged the pirates. There was brief fighting before they defeated them," Abdirizak Hared, the mayor of Bosasso port, told Reuters.

The Al-Khaleej had been carrying food and new cars for sale in Somalia when it was raided by pirates seven km (four miles) off Bosasso, in the Gulf of Aden on the northeast coast, on Monday.

It was the second rescue mission against pirates operating from the lawless country this month after French commandos swooped to arrest six pirates in the same area.

A surge in hijackings for ransom has made the waters off Somalia some of the world's most dangerous shipping zones.

After the Al-Khaleej was brought into Bosasso port under guard, a Reuters witness saw 16 crew members of Asian origin who appeared safe.

He also saw seven pirates in chains, three of them bleeding. Police escorted them to a waiting van and drove them away under tight security from the port in Puntland region.

The ship, and cars on it, showed bullet marks.

"DEATH PENALTY"

Puntland security minister Abdullahi Said Samatar said the seven pirates would face the death penalty in accordance with the semi-autonomous region's piracy laws.

"We arrested seven pirates. Three of them were wounded during the shootout. We will charge them. The penalty for piracy in our country is death. They will be killed," Samatar said.

He said 110 security officers had taken part in the operation to storm the ship. One was wounded.

Puntland is a relatively peaceful region in northern Somalia that runs its affairs independently from the chaotic south of the Horn of African country.

"Puntland has no means to arrest such pirates but after we failed to get any international help we were forced to storm the ship that was bringing in suppliers to Bosasso in order to free it," he added.

Over the weekend, pirates also seized a Spanish tuna fishing vessel with 26 people aboard.

Samatar said they have sent troops to free the Spanish boat held by other pirates near Garad port, in Indian Ocean waters off southeast Puntland.

"We have sent our troops towards the Spanish ship around Garad. We hope they will successfully release the boat the same way," he said.

A Spanish frigate is on its way to the area and Madrid has sent its ambassador to Kenya to help resolve the crisis.

Crew members of the boat from Spain's Basque region spoke to family members on Tuesday and told them they were being held by up to 10, well armed pirates, Spanish national radio reported.

(Writing by Wangui Kanina and Guled Mohamed; editing by Diana Abdallah) (For full Reuters Africa coverage and to have your say on the top issues, visit: http://africa.reuters.com/)

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