MOGADISHU, Nov 1, 2009 (AFP) - Two sailors were killed in an exchange of fire off the northeast coast of Somalia on Sunday, after apparently trying to attack a Norwegian warship, Somali officials and an EU naval commander said.

Three others were injured in the incident at around 1:00 am (2200 GMT Saturday) when fishing boats were stopped and checked at sea as part of efforts to combat piracy in the region, Somali officials said.

The incident occurred off the coast of Alula in Puntland province, the officials said.

The two dead fishermen were a Yemeni and a Somali, according to the governor of Puntland's Bari province, Muse Gele Farole.

"A Yemeni sailor and a Somali died and three others were injured, including two Yemenis," the governor told AFP.

A European Union naval commander said that a Norwegian warship came under heavy gunfire early Sunday as it inspected a dhow off the northeast Somali coast.

John Harbour, of the EU naval mission in the Gulf of Aden, Operation Atalanta, said the Norwegian sailors escaped unharmed.

But he added they returned fire in self-defence and he did not know if any of their attackers were injured.

Between five and seven men on board the boat fired on the Norwegian sailors with heavy weaponry and Kalashnikov rifles, said Harbour.

"These were not innocent fishermen, they were armed with heavy machine-guns and Kalashnikovs and were clearly up to no good," he said.

The HNOMS Fridjof Nansen was attacked 12 nautical miles east of Alula, said an earlier statement from the mission.

"The guys in the boarding party got a shock, because they had inspected three other dhows nearby, all anchored, and all of which cooperated," Harbour said.

"When they approached the fourth, they were fired upon - and clearly became nervous."

"The boarding party returned fire in self-defence " and retreated to 1,000 metres (yards), because their main job was to escort a World Food Programme aid ship which had to keep moving.

"You are talking about guys firing automatic weapons at you - you retreat to try and de-escalate the situation."

"We are not aware of any deaths or injuries on the dhow. They fired back to try and keep the heads of their attackers down."

"There was no indication that anybody had been hit - but there was no opportunity to return and assess the damage."

While Norway is not part of the 27-nation EU, it is a longstanding member of NATO - which collaborates with the Brussels-mandated mission on a host of interntional anti-piracy operations.

Said Muse, the deputy commander of security forces in Alula, earlier said French forces were thought to have been behind the attack.

"The wounded told us they were French forces who carried out the attack, but we are not sure yet," he said.

The chiefs of staff of the French armed forces denied any French involvement.