Media playback is unsupported on your device Media caption A minute's silence was observed at the Nagasaki Peace Park

An emotional memorial service has been held in the Japanese city of Nagasaki where US forces dropped an atomic bomb during World War Two, 70 years ago.

Speeches at the ceremony criticised the attending Prime Minister Shinzo Abe for his plans to loosen the restrictions on what Japan's military can do.

At least 70,000 people died in the attack, which came three days after another bomb was dropped on Hiroshima.

Nagasaki was only chosen after a cloud obscured the original target, Kokura.

A solemn ceremony in front of guests from 75 countries, including US Ambassador Caroline Kennedy, began on Sunday with a declaration read out by children.

Media playback is unsupported on your device Media caption Sumiteru Taniguchi was 16 when the atomic bomb was dropped on Nagasaki

A minute's silence and bells marked the time of the explosion in 1945 at 11:02 (02:02 GMT).

Nagasaki mayor Tomihisa Taue then delivered a peace declaration to the ceremony. He said there was "widespread unease" about Mr Abe's bid to alter the country's pacifist constitution.

A survivor of the Nagasaki attack, 86-year-old Sumiteru Taniguchi, described the injuries he had suffered and said he could not accept Mr Abe's new legislation.

The legislation would allow Japan to engage in combat - in defence of an ally which comes under attack - for the first time since World War Two.

Analysis: Rupert Wingfield-Hayes, BBC News, Tokyo

Image copyright AP

As the peace bell chimed, the people of Nagasaki stopped and bowed their heads remembering that moment 70 years ago when their city was destroyed in a blinding flash of white light.

Nagasaki often gets forgotten as the world focuses on Hiroshima. But the bomb dropped here was made from plutonium and was even more powerful.

Perhaps the most powerful moment in the ceremony came when survivor Sumiteru Taniguchi got up to speak. He described his own terrible injuries - of the skin hanging like rags from his arms and back.

But then he turned on Prime Minister Shinzo Abe sitting nearby. Do not meddle with Japan's pacifist constitution, he warned him. The audience erupted in loud clapping. Mr Abe looked straight ahead, showing no emotion.

In pictures: The Nagasaki bombing

In his address to the ceremony, Mr Abe said Japan remained "determined to pursue a world without nuclear weapons".

In a statement read out on his behalf, UN Secretary General Ban Ki-moon said: "Nagasaki must be the last - we cannot allow any future use of nuclear weapons. The humanitarian consequences are too great. No more Nagasakis. No more Hiroshimas."

Media playback is unsupported on your device Media caption Japanese PM Shinzo Abe called for the abolition of nuclear weapons

Image copyright AP Image caption At least 70,000 people died in the attack

Image copyright AP Image caption An image of the mushroom cloud from the bomb was projected on to a cathedral

The effects of the bomb were instant and devastating. It destroyed a third of the city, killing thousands instantly and condemning more to death from radiation sickness.

Days later, Japan surrendered, ending World War Two, although the necessity of the two bombs has been debated ever since.

"It was a clear, sunny day and there was a sudden, blinding flash," remembered one Nagasaki survivor, Toru Mine, who now guides visitors at a museum dedicated to the event.

"My first thought was that it should be a thunder, but I soon realised it's bizarre to have a thunder in a clear sky."

Mr Taniguchi still bears scars on his back, the remains of three ribs that half rotted after the bomb dropped protruding from his chest.

''While people around me were dying, I lived. People say I survived but I think I was kept alive. I am still suffering," he said.