A US court on Wednesday convicted five Somali men of piracy over a 2010 attack on a US naval ship in the corsair-infested waters off the Horn of Africa.

The five men were on a skiff that fired an AK-47 at the USS Ashland, a dock-landing vessel, which fired back with a 25mm machine gun, setting the pirates' ship on fire and killing one of its crew members.

The US vessel then deployed inflatable boats to rescue the others. There was no damage to the US ship and none of its crew were wounded.

Three of the men were alleged to have previously gone to sea on a separate raid in February 2010 before being intercepted by Britain's Royal Navy.

In November 2010 a Virginia court sentenced the alleged ringleader of the group to 30 years in a plea bargain under which he admitted to having attacked the Ashland using a firearm.

The five men convicted on Wednesday are to be sentenced July 1-2 on a range of charges that carry maximum punishments of 10 years to life in prison.

"These men were pirates -- plain and simple,' said US Attorney Neil MacBride of the Eastern District of Virginia.

"They attacked a ship hoping to hold it ransom for millions of dollars. Few crimes are older than piracy on the high seas, and today's verdict shows that the United States takes it very seriously."

In the last several years pirates based in lawless Somalia have carried out scores of high-profile sea hijackings, netting millions of dollars in ransom payments and driving up the costs of shipping along vital seaways.

The number of Somali pirate attacks is currently at a three-year low, thanks to beefed up naval patrols and teams of armed security guards aboard ships in the Gulf of Aden and the Indian Ocean.

However, the International Maritime Bureau (IMB) warns that Somalia's waters remain extremely high-risk.

Eight boats and 139 hostages are still held by Somali pirates, according to the IMB, while some pirates have turned to land-based kidnapping and banditry.