By Jonathan Saul
LONDON (Reuters) - Al Qaeda's Yemen branch remains a powerful force and poses a growing risk to merchant ships in vital waterways nearby despite efforts by Yemeni government forces and their allies to push back the group, a top officer in an international naval force said.
Al Qaeda in the Arabian Peninsula (AQAP) confirmed on Saturday it had withdrawn from the southern Yemeni port of Mukalla - a week after Yemeni government and Emirati soldiers seized the city that was used by the Islamist militants to amass a fortune.
Captain William Nault, Chief of Staff with the multi-national Combined Maritime Forces (CMF), told Reuters the gains by government forces were "heartening" and a "setback" for AQAP, but added the group still had capabilities due to the ongoing civil war.
"AQAP has taken advantage of that chaos and moved into the void. In doing so they have gotten stronger," said Nault of CMF, whose mission includes counter-piracy and counter-terrorism in the region.
AQAP has exploited conflict between Yemeni government loyalists backed by a Gulf Arab coalition and Houthi rebels allied to Iran and has sought to carve out a quasi state.
The group still controls the Arabian Sea towns of Zinjibar and Shaqra, about 400 km (250 miles) southwest of Mukalla.
That coastal area is close to the Bab al-Mandab gateway though which nearly four million barrels of oil are shipped daily to Europe, the United States and Asia.
Nault said AQAP had a "stated capability and intent to conduct a maritime terrorist attack", which was something "we look at very hard".
"I would assess that as getting worse over the last year instead of better," he said on a visit to London.
"That threat would be against a soft target meaning an industry ship passing or going in and out of ... the Red Sea towards the eastern end of Yemen."
Yemen has a 1,900-km (1,180 mile) coastline that also juts into the Gulf of Aden and Red Sea, a vast area to police given international navies were already stretched combating Somali piracy in the region, which had been contained in recent years.
AQAP has planned several foiled bombing attempts on Western-bound airliners and claimed credit for the 2015 attack at the Charlie Hebdo magazine offices in Paris.
Al Qaeda bombed the USS Cole warship in October 2000 when it was docked in Aden, killing 17 U.S. sailors. Two years later an al Qaeda attack damaged a French tanker in the Gulf of Aden.
Nault said there was also the possibility of piracy re-emerging around Yemen, which may involve militants. "That is my concern - will we see a resurgence of piracy-like activity ... it might be something else in that area around Yemen."
(Editing by Dominic Evans)