TOKYO (AP) _ Japan's top police official, who is leading the investigation into a deadly nerve gas attack on Tokyo's subways, was shot and wounded by a masked man on a bicycle as he left his apartment for work Thursday morning.

It wasn't clear whether the shooting of Takaji Kunimatsu, head of the National Police Agency, was related to the attack on Tokyo's subways last week that killed 10 people and sickened 5,000 others.

Kunimatsu was hit by four bullets and hospitalized in serious condition, said Tadatoshi Honda, spokesman for the police precinct where the shooting took place. Two hours later, doctors had removed two bullets. Another bullet passed through his body, Honda said.

No one has claimed responsibility for the subway killings, but they are believed to have been directed at police because all of the trains that were gassed were to have stopped at the station beside the National Police Agency.

There was no immediate claim of responsibility for shooting Kunimatsu, who is 57 and became chief of the police agency in July after holding key posts that made him a central figure in crackdowns on organized crime. He has been a member of the police agency since 1961.

The gunman, who was wearing a black coat and a surgical mask to hide his face, escaped after shooting Kunimatsu as he left his high-rise condominium, police said. Police began hunting for the gunman immediately.

Kunimatsu had no bodyguards, Honda said. There were no other injuries.

Guns are strictly banned in Japan, and attacks on police are rare. The recent spate of violence has deeply unnerved both the government and the public at large.

``This is an attack on our authority,'' said Hiromu Nonaka, head of the government's National Public Safety Commission. ``We must do our utmost to find the culprit.''

At Kunimatsu's condominium, dozens of police investigators surrounded the building, searching for clues and holding back a growing crowd of reporters and cameramen.

Police launched their biggest search operation ever after the subway deaths, mobilizing thousands of officers for investigations of several sites used by a doomsday religious group that has been linked to the kind of nerve gas that was unleashed on the subways.

Tons of chemicals, including all of the ingredients necessary to make the nerve gas, have been seized in the searches, but no charges have been filed yet.

The group, called Aum Shinrikyo or Supreme Truth, denies any connection with the subway deaths. A member of the group contacted by The Associated Press refused to comment on Thursday's shooting.