Somali pirates hijacked three Thai fishing vessels with 77 crew aboard more than 1,900 km off the Somali coast, the farthest-off-shore attack to date, the EU Naval Force said on Tuesday.

Pirates have expanded their range south and east in response to an increase in patrols by European and U.S. warships off the Somali shore.

The hijacking of the three Thai vessels on Sunday was almost about 1000 km outside the normal operation area for the EU Naval Force, said its spokesman, Cmdr. John Harbour.

The EU Naval Force said the attack so far out at sea was a clear indication that the EU, NATO and U.S.—led anti-piracy missions were having a “marked effect on pirate activity in the area.”

“Once they start attacking that far out, you’re not even really talking about the Somali basin or areas of water that have any connection with Somalia,” said Roger Middleton, a piracy expert at the British think tank Chatham House. “Once you’re that far out it’s just the Indian Ocean, and it means you’re looking at trade going from the Gulf to Asia, from Asia to southern Africa.”

The three vessels — the MV Prantalay 11, 12, and 14 — have 77 crew onboard in total. All the crew are Thai, Cmdr. Harbour said. The owner of the vessels is PT Interfishery.

Before the latest hijackings pirates held 11 vessels and 228 crew, said Cyrus Mody of the International Maritime Bureau. The latest hijacking raises those numbers to 14 vessels and 305 crew.

Pirates have increased attacks against shipping vessels over the last year in hopes of netting the multi-million dollar ransoms they can earn. Because of increased naval patrols and increased defences on board commercial vessels, the pirates’ success rate has gone down, though the number of successful attacks has stayed about the same year over year.

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