The Indian Navy said Saturday that it is shadowing a bulk carrier that was boarded by unknown attackers — likely Somali pirates — in the Arabian Sea.

The Maltese-flagged MV Ruen, with a crew of 18, had sent a Mayday message on the United Kingdom Maritime Trade Operations portal on Thursday indicating that six unknown people had boarded the vessel, the Indian Navy said in its statement.

The navy responded to the distress call by sending its anti-piracy patrol warship and maritime patrol aircraft to locate and assist the vessel, it added.

The aircraft overflew the hijacked vessel early Friday and has since been continuously monitoring the movement of the vessel, which the Indian Navy said was headed toward the coast of Somalia. It added that its warship, which was deployed in the Gulf of Aden for anti-piracy patrols, also intercepted the carrier early on Saturday.

The Ruen, which is managed by Bulgarian shipping company Navibulgar, was off the Yemeni island of Socotra when it was boarded on Thursday, the private intelligence firm Ambrey and the UKMTO said. Bulgarian authorities said the ship’s crew were nationals of Angola, Bulgaria and Myanmar.

“The necessary steps have been taken to pass the information on to all foreign partners and institutions that we will count on to provide assistance,” Bulgarian Foreign Minister Maria Gabriel told reporters Friday.

No group immediately claimed responsibility for the assault. However, suspicion immediately fell on pirates from Somalia. Their activity has dropped in recent years, but there has been growing concern it could resume amid the political uncertainty in the country and wider chaos in the region that has included attacks on shipping by Yemeni Houthi rebels.

On Friday, the UKMTO issued a warning to shippers saying the security manager for the Ruen “believes the crew no longer has control of the vessel.” The European Union’s anti-piracy force in the region said the Spanish frigate Victoria was on its way to intercept the “alleged pirate-hijacked vessel.”