Activists have regularly attacked the Japanese with "stink bombs"

Paul Watson, of the Sea Shepherd group, said his colleagues had been throwing stink bombs, but the Japanese responded with "flash grenades" and gunfire.

He said he felt a thud in his chest and found a bullet in his Kevlar vest.

But Tokyo denied any bullets had been fired, saying "warning devices" were thrown after their ship was attacked.

The foreign ministry said the Japanese coastguard on board the Nisshin Maru ship had thrown a baseball-sized device, which exploded near the activists' ship emitting a loud noise.

The device was not designed to hurt people, and the ministry said it was not aware of any injuries.

'Aimed at us'

Mr Watson told Australian radio that he found a bullet in his Kevlar vest.

"It bruised my shoulder but it would have hit my heart if I didn't have the vest," he said.

Mr Watson is captain of the Sea Shepherd vessel, the Steve Irwin

He told Australia's ABC News that there was no justification for the whalers opening fire.

"We were doing what we usually do, which is putting stink bombs on deck," he said.

"We go out of our way to make sure we don't throw them near anybody, but they were throwing the flash grenades directly at us."

Japan had planned to kill up to 900 minke whales and 50 fin whales during the expedition.

Tokyo says it carries out whaling for scientific research, but critics say the same data can be collected without killing the animals.