TOKYO - Japan's prime minister, fighting criticism at home over his handling of the aftermath of the March 11 earthquake and tsunami, says he deeply regrets the crisis at a radiation-leaking nuclear plant.

In a commentary seen in the weekend edition of the International Herald Tribune, Prime Minister Naoto Kan also pledged to investigate the cause of the nuclear crisis and to improve efforts to share information about the situation at the Fukushima Dai-ichi plant.

Kan said bringing the crisis under control was his "top priority."

The commentary also appeared in the New York Times and Washington Post.

Levels of radioactivity have risen sharply in seawater near the plant in northern Japan, signaling the possibility of new leaks at the facility.

Special Coverage:Earthquake Hits Japan  When disaster strikes