Somali pirates attacked a 26,000-tonne, Panama-flagged bulk carrier in the Gulf of Aden today, but were driven away by sailors spraying them with water-hoses, NATO alliance staff said.

The NATO officials, on board a Portuguese warship protecting shipping lanes from piracy, said an unexploded rocket-propelled grenade landed in the commanding officer's cabin during the attack and bullets were fired at the ship.

The pirates left after water hoses were turned on them, NATO staff officer Stephan Gresmak said.

"They looked for an easier target," he told a Reuters reporter on the Portuguese ship NRB Corte-Real.

Eight pirates, armed with AK-47s, were on board the skiff that attacked the MV Anatolia soon after daybreak in the southwest corner of the Gulf of Aden, the officials said.

The Anatolia also used evasive steering to escape.

"It was on later inspection the Commanding Officer saw the bullet holes in the superstructure (outer skin) of the ship," Gresmak said. "The Commanding Officer reported an unexploded RPG round in his cabin to the UK Maritime Shipping Centre, and they advised not to touch it."

Somalis wreaked havoc in the Gulf of Aden last year, but due to increased naval patrols there have mainly moved operations this year into the Indian Ocean.