(AFP) - Indian Ocean naval forces said Monday they had freed two fishing vessels hijacked separately by Somali pirates, with Indian sailors rescuing an Iranian boat and commandos from the Seychelles releasing a Sri Lankan trawler.

The hijackings off Somalia have fuelled concerns about a resurgence of Indian Ocean raids by opportunistic pirates, coming on top of a separate surge of attacks launched by Yemen's Iran-backed Huthi rebels.

Huthi gunmen have launched scores of attacks in the Red Sea and Gulf of Aden targeting Israeli-linked vessels in response to Israel's war against the Palestinian militant group Hamas in Gaza.

International naval forces have been diverted north from the Gulf of Aden into the Red Sea, sparking fears that pirates will exploit the security gap, with the first successful case of Somali piracy since 2017 recorded in December.

Pirate attacks off the Somali coast peaked in 2011 -- with gunmen launching attacks as far as 3,655 kilometres (2,270 miles) from the Somali coast in the Indian Ocean -- before falling off sharply after international navies sent warships and commercial shipping deployed armed guards.

- 'Utmost courage' -

India's navy said it had deployed its warship INS Sumitra -- which was on anti-piracy patrol off the east coast of Somalia in the Gulf of Aden -- after receiving a distress message from the Iranian-flagged fishing vessel Iman.

"The fishing vessel had been boarded by pirates and the crew taken as hostages," Indian navy spokesman Commander Vivek Madhwal said, adding that the warship intercepted the boat and then worked to "coerce" the hijackers.

The warship "ensured the successful release of all 17 crew members along with the boat", he added, with the fishing boat then "sanitised and released for onward transit".

The navy, which released photographs of the Iranian fishing boat and crew, as well as its sailors towing a skiff, did not give further details of the operation or fate of the pirates.

Separately, Seychelles forces freed a Sri Lankan vessel "hijacked by armed Somali pirates", President Wavel Ramkalawan's office said Monday.

The Sri Lankan fishing trawler Lorenzo Putha-4 was seized along with its six-man crew on Saturday, about 840 nautical miles (1,555 km) southeast of Somalia's capital Mogadishu.

"Seychellois special military forces boarded the boat with utmost courage to take complete control of the vessel and rescue our Sri Lankan brothers," the presidency said in a statement.

Sri Lankan navy spokesman Gayan Wickramasuriya told AFP the six crew were safe and that three pirates had been detained.

- 'Piracy of opportunity'? -

Eric Jaslin, the head of France-based Maritime Information Cooperation and Awareness (MICA) Center, said last month it was still too early to say if attacks were the result of "piracy of opportunity" or because military resources were "focused on the Red Sea".

India's navy has been deployed continuously off Somalia since 2008, but in December sent a far larger force -- including three guided-missile destroyers and P-8I reconnaissance aircraft to "maintain a deterrent presence".

India, which has close trade ties with Iran, has not joined the US-led maritime task force in the Red Sea to protect international shipping against attacks by the Tehran-backed Huthi rebels.

On January 5, Indian navy commandos in the Arabian Sea boarded the Liberian-flagged bulk carrier MV Lila Norfolk after a failed hijacking attempt.

Last month, Somali pirates hijacked the bulk carrier MV Ruen.

The Bulgaria-owned and Malta-flagged vessel was seized by Somali pirates 380 nautical miles east of the Yemeni island of Socotra on December 16.

The pirates, who released one injured sailor into the care of the Indian navy, took the MV Ruen and its remaining 17 crew members to Somalia's semi-autonomous state of Puntland.

© Agence France-Presse