New Zealand's anti-whaling activist Pete Bethune said he has no regrets about taking the action that led to him spending time behind bars in Japan, and has not decided whether to return to Antarctica to protest.

Bethune returned to New Zealand on Saturday after being deported from Japan, where he'd been in jail since his arrest in February and had on Wednesday received a two-year suspended jail sentence.

At Auckland Airport, Bethune said he had been worried he would be sentenced to a prison term and is hugely relieved to be home, Radio New Zealand reported on Saturday.

Bethune said his last month in prison awaiting trial started to grind him down.

Bethune is calling on the New Zealand government to take a stronger stand against illegal whaling, saying New Zealand in the past used to stand up to other countries about big issues.

The 45-year-old was the captain of the powerboat the Ady Gil, which was damaged in a collision with the Japanese fleet's security ship Shonan Maru II on 6 January in the Southern Ocean and sank soon after.

On Feb. 11, Bethune boarded a Japanese whaling vessel and attempted to make a citizen's arrest of its captain.

A Tokyo court on Wednesday found him guilty of five charges related to boarding the vessel. He admitted four charges, including vandalism and carrying a knife, but denied a charge of assault.