The attack came three days after the world's first atomic bomb

The Japanese city of Nagasaki is marking the 60th anniversary of its destruction by a US atomic bomb at the end of World War Two.

At least 70,000 people died in the world's second nuclear bomb.

About 6,000 people attended a ceremony in the city's peace park, including Prime Minister Junichiro Koizumi.

Correspondents say there is fresh controversy over why the attack happened just three days after the bombing of the city of Hiroshima.

Some historians argue that the attack was seen as necessary because Japan had not surrendered, reports the BBC's Adam Brookes in Washington.

But others believe that the attack enabled the American military to try out plutonium as a nuclear weapon.

Nuclear opposition

Mr Koizumi took part in the official commemoration on Tuesday, which also saw a memorial Mass in the city's Catholic cathedral.

"This is an occasion to remember the victims, and pray for world peace," he said.

A peace bell rang out as the city marked the exact moment 60 years ago when a US plane dropped the bomb nicknamed "Fat Man" for its rotund shape.

Catholics in the city will also remember the victims

The city's citizens still question whether the Americans were justified in targeting their city for the second atomic attack.

The bomb used plutonium as its core - unlike the one dropped on Hiroshima, which used uranium.

Nagasaki's mayor says he believes they were the victims of what in effect was a deadly nuclear test.

Iccho Ito asked US citizens whether their security was enhanced by their nuclear arsenal.

And he appealed to them to join hands with others to work together for a peaceful planet free from the threat of the nuclear bomb.

"We are confident that the vast majority of you desire in your hearts the elimination of nuclear arms," he said.

Overshadowed

The bomb dropped on Nagasaki exploded with a force equivalent to 21,000 tonnes of conventional explosive.

Plutonium is much more powerful than the uranium bomb dropped on Hiroshima.

Most of those killed in the second attack were melted or burnt to death immediately.

However, correspondents say that Nagasaki's tragedy has long been overshadowed by that of Hiroshima, where about 140,000 people were killed by the bomb and its aftermath.