The supplies, arranged by supporters of the Tamil rebel cause, were loaded onto a ship in the English port of Ipswich in April -- just weeks before the government declared victory in the ethnic conflict, a navy spokesman said.
"We have seized the vessel and we are bringing it ashore now," Captain D.K. Dassanayake said, adding the crew offered no resistance when the navy boarded the vessel 140 kilometres (87 miles) west of Sri Lanka.
The ship, the Captain Ali, was carrying hundreds of tonnes of food, medicine and other supplies for Tamil civilians caught up in the decades-long conflict, he said.
A London-based group called Mercy Mission to Wani had arranged the transport of the supplies at a time when Tamil Tiger rebels were cornered in a strip of coastline in the island's northeast and using tens of thousands of civilians as cover.
Wani had formed part of the Tigers' virtual mini-state in the island's northeast before the end of the conflict.
"We have been tracking this s