A merchant ship has exchanged fire with assailants on a small craft in a busy shipping lane in the Indian Ocean, according to an arm of the Royal Navy’s Maritime Trade Operations.

UKMTO said the ship was approached by a small armed vessel some 780 nautical miles (1,400 km) east of Hafun, Somalia, which would make it one of the southernmost attacks on shipping since Yemen’s Houthi rebels began targeting vessels and Somali piracy resurfaced.

The craft had four armed people on board who were armed with automatic rifles and a rocket-propelled grenade launcher.

A security team on the merchant ship fired warning shots when the craft was 300 metres away, which was followed by an “exchange of fire” before the apparent pirates retreated.

Ambrey Analytics, a maritime security firm, said the small craft was a blue and grey, Somali-style skiff and the suspects were not wearing military fatigues.

“Vessel and crew are safe and continuing to next port of call,” UKMTO said. “Vessels are advised to transit with caution and report any suspicious activity.”

The targeted vessel was not identified, but Ambrey and maritime security firm Diaplous Group said the incident involved a bulk carrier.

Vessel tracking data shows no bulker at the exact location identified by the firm and the Royal Navy agency, but several were in the general vicinity on a trade lane that is used by ships crossing the Arabian Sea between the Suez Canal and the Far East.

The incident appears to bear the hallmarks of Somali piracy but is far from the country’s shore — or any coastline for that matter.

That would make it nearly impossible for a small craft to operate on its own, but Diaplous said it retreated to a larger mothership.

The location also puts it outside of the area of the Indian Ocean, which Lloyd’s of London Joint War Committee has identified for war-risk insurance, according to Ambrey.

After a long dormancy, Somali piracy reemerged late in November, shortly after the Houthis began targeting ships in the Red Sea and Gulf of Aden. Hijacked in the highest-profile incident, Navibulgar’s 41,600-dwt bulker Ruen (built 2016) has been held for ransom since 14 December.

Saturday’s firefight comes just days after Brazil took command of Combined Task Force 151, a coalition of navies including the US, Seychelles, Djibouti and the United Arab Emirates that patrols the Gulf of Aden to protect shipping from piracy in coordination with the European Union Naval Force.