Five groups of pirates may be operating off the coast of Somalia with more attacks possible as the weather in the region improves, the EU naval force warns.

No attacks have been reported for more than two weeks but the changing conditions are likely to suit groups aiming to board ships, according to the latest anti-piracy bulletin by Operation Atalanta, the EU mission in the region.

Pirates are likely to be operating in the Gulf of Aden and Somali Basin from “mother boats” and scouting for targets in areas with better sea conditions, it said. The remote locations are less likely to be patrolled by international forces, it added.

“The end of the monsoon period is likely to facilitate pirates’ boarding activities,” it said. “Ships operating in the area are advised to increase vigilance.”

The International Maritime Organization has also warned of a potential increase in cases of pirates targeting vessels forced to divert from the Red Sea, owing to Houthi missile attacks.

IMO secretary general Arsenio Dominguez said the organisation had spoken with authorities in East and West Africa to warn of the threat.

The rising tensions in the Red Sea have coincided with the relaunch of piracy off Somalia as Western naval forces are focused on tackling the Iran-backed threat of the Houthis.

Ship transits and cargo volumes via the Cape of Good Hope in the first 11 days of February increased by about 75% from the same time last year, according to Portwatch, an International Monetary Fund and Oxford University collaboration.

Somali pirates completed their first successful hijack in six years in December, when they seized the 41,600-dwt Bulgarian handymax bulker Ruen (built 2016) with 18 crew members. Negotiations continue for the release of the Navibulgar-owned ship.