The United States has warned military and commercial vessels plying the coast of Yemen that they may be targeted by Al-Qaeda, citing the 2000 attack on the USS Cole.

"Information suggests that Al-Qaeda remains interested in maritime attacks in the Bab-al-Mandeb Strait, Red Sea, and the Gulf of Aden along the coast of Yemen," a "special advisory" on the website of the US Office of Naval Intelligence said.

The advisory by the US Department of Transportation said although it was unclear how the attacks would occur, "it may be similar in nature to the attacks against the USS Cole in October 2000 and the M/V Limburg in October 2002 where a small to mid-size boat laden with explosives was detonated."

Seventeen US sailors were killed in the October 2000 bombing of the USS Cole in the Yemeni port of Aden, attributed to Al-Qaeda.

Two years later, the French-registered supertanker Limburg was damaged in the Gulf of Aden, also attributed to an Al-Qaeda attack.

The advisory cautioned about other, more sophisticated methods of attack, including missiles or projectiles.

"Although the time and location of such an attack are unknown, ships in the Red Sea, Bab-al-Mandeb Strait, and the Gulf of Aden along the coast of Yemen are at the greatest risk of becoming targets of such an attack," it said.

All vessels transiting the waters in the vicintity of Yemen were urged to operate at a "heightened state of readiness, maintain strict 24-hour visual and radar watches, and regularly report their position, course and speed to the UKMTO," the UK Maritime Trade Operations (UKMTO), which has an office in Dubai.

"Vessels are at greatest risk in areas of restricted maneuverability, and while in/near port or at anchor. Merchant vessels are requested to report any suspicious activity to the UKMTO Dubai."

Yemen's interior ministry said last week it had beefed up security around oil and maritime installations in case of retaliation by Al-Qaeda after several strikes against the jihadist network.

"Yemeni authorities have increased security measures around oil and maritime installations, in addition to securing the routes of oil tankers," the ministry website said.

"Firm orders have been given to security bodies and the coast guard to up their alert levels in order to counter any possible terror attack by Al-Qaeda elements," it added.

It said that attacks could take place "in retaliation for the qualitative and severe strikes that targeted terror hideouts in several provinces."

Al-Qaeda in the past has targeted oil facilities in Yemen, which produces almost 300,000 barrels of oil a day, more than half of which is exported.

The impoverished country also has a gas terminal in Balhaf, in the south.

Yemen has intensified operations against the local Al-Qaeda branch since December.

The United States has reportedly supplied Yemen with intelligence and other support in its operations against the jihadists.