The mayor of the Japanese city of Nagasaki died in the early hours of Wednesday after being shot in a brazen attack by a man police say was an organized crime chief.

Itcho Ito, 61, was shot twice in the back at point-blank range outside a train station on Tuesday evening, said Nagasaki police.

One of the bullets struck Ito's heart and he went into cardiac arrest, according to Nagasaki University Hospital spokesperson Kenzo Kusano. He was on life support after undergoing an emergency operation. But public broadcaster NHK reported early Wednesday morning local time that Ito died of his injuries.

Police said Tetsuya Shiroo, a senior member of Japan's largest organized crime syndicate, was wrestled to the ground by officers after the attack and arrested for attempted murder.

Shiroo later admitted to shooting Ito with a handgun with the intent to kill, Nagasaki chief investigator Kazuki Umebayashi said at a news conference.

Prime Minister Shinzo Abe released a statement late Tuesday calling for a "rigorous investigation."

In 2003, Shiroo reportedly clashed with Nagasaki city officials after his car was damaged when he drove into a hole at a public works site. He tried to get compensation from the city after his insurance company refused to pay up, but he was unsuccessful, according to NHK.

Kyodo news agency also reported that Shiroo sent a letter to broadcaster TV Asahi to protest recent money scandals linked to Ito -- including hidden accounts and public works contracts.

Backed by the ruling Liberal Democratic Party, Ito was campaigning for his fourth term in office before Sunday's elections.

He was an active figure in the movement against nuclear proliferation, heading a coalition of Japanese cities calling for the elimination of nuclear weapons.

Only four politicians are known to have been killed since World War II. But this was the second attack in the last 20 years against a mayor of Nagasaki. In 1990, Mayor Hitoshi Motoshima was shot and seriously wounded after saying that Japan's emperor bore some responsibility for World War II.

The shooting is rare in a country where handguns are strictly banned. Illegal firearms are mostly in the hands of gangsters, or "yakuza."

Organized crime groups are behind most shootings in Japan, with two-thirds of the country's 53 known shootings last year being gang-related, according to the National Police Agency. Police estimate there are about 84,500 gangsters across Japan.

The yakuza also have had a long-standing political alliance with right-wing nationalists in Japan But authorities did not indicate that Tuesday's attack was politically motivated.

With a report from the Associated Press