New Zealand has sharply criticized Japan for allowing a whaling ship to enter New Zealand's economic waters.

New Zealand said Monday that Japan ignored requests that the Shonan Maru 2 steer clear of New Zealand's 200-nautical-mile Exclusive Economic Zone (EEZ) as the whaler pursued an anti-whaling vessel operated by protest group Sea Shepherd.

The incident comes during heightened tensions over whaling. Last week, a different Japanese whaling ship and a second Sea Shepherd boat collided in the icy seas off Antarctica, with both sides blaming each other for the crash.

New Zealand Foreign Minister Murray McCully said Japan's latest actions were "unhelpful, disrespectful and short-sighted" and on Monday summoned Japan's ambassador Yasuaki Nogawa to meet with a senior official, who McCully said expressed New Zealand's "deep disappointment."

"The New Zealand Embassy in Tokyo last week made it very clear we did not want members of the Japanese whaling fleet entering our EEZ," McCully said, adding "New Zealand's strong opposition to Japanese whaling in the Southern Ocean is well known and further action may be taken."

He didn't elaborate on what that action might entail.

The Japanese Embassy declined immediate comment Monday.

Glenn Inwood, a spokesman for the Institute of Cetacean Research, which is funded by the Japanese government, said every vessel has a right to enter another country's economic waters and New Zealand's request for the boat to stay away was not legally enforceable.

He said the Shonan Maru 2 was monitoring the Sea Shepherd protest boat Steve Irwin following harassment near Antarctica.

"It's important for their own safety to know exactly where the Sea Shepherd pirate vessels are at all times," Inwood said.

Speaking by satellite phone from the Steve Irwin, captain Siddharth Chakravarty said his organization abides by the law and is simply trying to prevent the unwarranted slaughter of whales. He said the Shonan Maru 2 had been tailing their boat for a week.

Under the provisions of a United Nations treaty that has been signed by more than 160 countries including New Zealand and Japan, each country has certain sovereign rights over their economic zone. Those rights are not as strong as the rights for territorial waters, which extend 12 nautical miles from the shore.

The Southern Hemisphere whaling season typically runs through the end of March.