NAGASAKI, Japan (Asahi Shimbun) - Nagasaki Mayor Iccho Itoh died early Wednesday after being shot in the back twice Tuesday night in front of his campaign office where he had just returned after stumping for Sunday's election.

The 61-year-old mayor was unconscious and in critical condition, and he was pronounced dead at a hospital at 2:28 a.m. Wednesday, officials said. He was treated in the intensive care unit at the Nagasaki University Hospital.

The suspected gunman was overpowered by people at the scene near JR Nagasaki Station.

Police arrested the man, Tetsuya Shiroo, 59, a senior member of a yakuza gang affiliated with the Yamaguchi-gumi, on suspicion of murder.

Shiroo told police he shot Itoh, but he has not explained the motive for the attack, police said, adding that they had confiscated a firearm.

The attack occurred at around 7:50 p.m. Tuesday. A witness said he heard two shots and a woman scream. "I was working when a colleague said there might have been a shooting," the witness said. "And when I went out, I saw a guy and a woman holding down a man in black clothes on his stomach at a pedestrian crossing."

The witness said the man was holding a gun. Prime Minister Shinzo Abe told reporters in Tokyo after the shooting, "I want investigative authorities to conduct a thorough investigation and reveal the truth."

Itoh, mayor of the second city hit by an atomic bomb, has won international recognition for his promotion of nuclear disarmament.

He is running in the mayoral election Sunday for a fourth term.

Itoh won a seat on the Nagasaki city assembly for the first time in 1975. He later served as a prefectural assembly member before running and winning the mayoral election in April 1995.

He has since been re-elected twice, in 1999 and in 2003.

In January 1990, Itoh's predecessor, Hitoshi Motoshima, was shot by a member of a right-wing organization in front of Nagasaki city hall, a year after the death of Emperor Hirohito, posthumously known as Emperor Showa.

The shooter told police he was unhappy with Motoshima for saying that the emperor was responsible for the war.

Motoshima, who recovered from the attack, ran for his fifth term and lost to Itoh in 1995.

"I am shocked," Motoshima, 85, said Tuesday night about the latest shooting. "I wonder why Itoh was targeted.

"Above all, violence should never be allowed," he said.