Japan's Prime Minister has called for “a world free of nuclear weapons” at a ceremony to mark the 72nd anniversary of the Hiroshima bombing.

Shinzo Abe said existing non-proliferation treaties should be strengthened, and pledged Japan would make “utmost efforts for the realisation of eternal world peace".

The country was marking the date more than seven decades since the US dropped an atomic bomb on Hiroshima, which detonated 600 metres above the city, killing 140,000 and effectively ending the Second World War.

The event at Peace Memorial Park, near Hiroshima's ground zero, was attended by 50,000 people and representatives from 80 nations and the EU, according to The Japan Times.

However, the commemoration has been overshadowed by the escalating threat posed by North Korea.

Last month its military tested two intercontinental ballistic missiles with major US cities such as Los Angeles and Chicago within range of attack, though it is unclear if they could be armed with nuclear warheads.

"This hell is not a thing of the past," Hiroshima Mayor Kazumi Matsui said at Sunday's commemoration ceremony. "As long as nuclear weapons exist and policymakers threaten their use, their horror could leap into our present at any moment.

“You could find yourself suffering their cruelty."

After the bombs dropped: Hiroshima and Nagasaki Show all 19 1 /19 After the bombs dropped: Hiroshima and Nagasaki After the bombs dropped: Hiroshima and Nagasaki 424444.bin After the bombs dropped: Hiroshima and Nagasaki 424445.bin Hiroshima: Cap of a mobilised student 2,200m from the hypocentre Tetsuo Manabe was a second-year student at a junior high school. He was exposed to the A-bomb while guarding his school as a member of a school defence squad, which comprised first and second-year students living in the neighbourhood. He was treated at a relief station, but died the following month. Donated by Mitsuko Yoshioka After the bombs dropped: Hiroshima and Nagasaki 424488.bin Hiroshima: A wrist watch One of the many clocks which stopped immediately after the A-bomb went off on August 6 1945. After the bombs dropped: Hiroshima and Nagasaki 424462.bin Hiroshima: Lunchbox (Replica) 550m from the hypocentre Reiko Watanabe (then 12) was a first-year student at First Municipal Girls' High School. She was exposed to the A-bomb during building demolition work. This lunchbox was found later near the work site, but her body was never found. The contents of the box, which Reiko never ate, were scorched black. Approximately 7,200 of the mobilised students in Hiroshima were killed by the atomic bomb. Donated by Shigeru Watanbe After the bombs dropped: Hiroshima and Nagasaki 424446.bin Hiroshima: Student's shirt 500m from the hypocentre Mutsuko Shimogouchi, a third-year student at Shintoku Girls' High School, was on the road in front of Shirakami Shrine when she was exposed to the A-bomb. Seriously burnt on her face, she soaked herself in a river for a while to ease the unbearable heat. On the way home, she was briefly treated at a primary-school-turned-temporary-rescue-station. She reached home in the evening of the same day with her face covered by gauze. She could be identified only by the name tag sewn onto the left side of her blouse. Two days later, she passed away. Donated by Chizuno Shimogouchi After the bombs dropped: Hiroshima and Nagasaki 424449.bin Nagasaki: Blouse made of summer Kimono cloth 800m from the hypocentre Miyako Tanube was exposed at Keiho Junior High School and died on the morning of 16th August, seven days after the bombing. On the day of the bombing, Miyako wore this blouse, which she made herself from her mother's summer kimono (a traditional Japanese garment). Her mother had to tear the left side of the blouse off Miyako's body because she was disabled by the serious burns and a bone fracture that she had suffered. Donated by Fuji Tanabe After the bombs dropped: Hiroshima and Nagasaki 424464.bin Hiroshima: Exposed plates 700m from the hypocentre This plate was found in the rubble near to the city centre. Some white substance is fused with the plate from the heat rays of the atomic bomb. After the bombs dropped: Hiroshima and Nagasaki 424454.bin Nagasaki: Exposed roof tile The surface of ceramic roof tiles exposed directly to the flash of heat instantly boiled and then hardened, leaving a distinctive bubbled texture. The bubbling was greater the shorter the distance from the hypocentre, reflecting the unimaginable ferocity of the atomic bomb heat rays. After the bombs dropped: Hiroshima and Nagasaki 424463.bin Nagasaki: Deformed glass container 350m from the hypocentre This glass container was donated in memory of a young girl who died after the bomb dropped. Her parents' house was 350 metres from the hypocentre. Her father, who was out at the time, survived, but her mother perished. Donated by Matsu Ogasawara After the bombs dropped: Hiroshima and Nagasaki 424450.bin Nagasaki: Rosary 500m from the hypocentre At the time of the explosion, more than ten parishioners were attending a mass in the chapel of Urakami Cathedral. All of them were trapped under the building and killed instantly. This rosary was with one of the parishioners. Donated by Ichiro Fukahori After the bombs dropped: Hiroshima and Nagasaki 424481.bin Nagasaki: Melted crucifix This melted crucifix was unearthed during the construction of a house in the region. After the bombs dropped: Hiroshima and Nagasaki 424441.bin Hiroshima: Pocket Watch (Replica) 1,600m from the epicentre Kengo Nikawa (then 59) was exposed to the A-bomb while heading for his assigned building demolition site in the city centre, where work was being carried out to create a fire lane to prevent the spread of fire in the event of an air raid. Burned from his right shoulder to his back and head, he died on August 22nd. This watch, a treasured gift from his son Kazuo, stayed with him whenever he went. Donated by Kazuo Nikawa After the bombs dropped: Hiroshima and Nagasaki 424482.bin Hiroshima: Glass bottle The extreme heat of the fire ignited by the A-bomb softened and deformed this glass bottle. After the bombs dropped: Hiroshima and Nagasaki 424495.bin 6th August 1945: An aerial view of the atomic bomb damage at Hiroshima. Getty Images After the bombs dropped: Hiroshima and Nagasaki 424497.bin The aftermath of the atom bomb dropped on Hiroshima, Japan, by the Americans at the end of World War II. The occupants of the burned-out bus were all killed. Getty Images After the bombs dropped: Hiroshima and Nagasaki 424499.bin Hiroshima after the atom bomb explosion. Getty Images After the bombs dropped: Hiroshima and Nagasaki 424500.bin This picture dated August 1945 in the Mariana Islands shows the US crew of the B-29 'Enola Gay' plane, including pilot Paul W. TIbbets (C), which dropped an atomic bomb on Hiroshima, Japan on 06 August 1945. Getty Images After the bombs dropped: Hiroshima and Nagasaki 424501.bin Colonel Paul Tibbets Jr, the pilot of the B-29 bomber 'Enola Gay', which dropped the atomic bomb on Hiroshima waves from the cockpit before takeoff. Getty Images After the bombs dropped: Hiroshima and Nagasaki 424502.bin A bombed out landscape in Hiroshima, Japan, following the explosion of the first atomic bomb. A few remaining buildings stand guard in a completely devastated area scattered with debris. Getty Images

If a nuclear bomb was dropped today it could cause greater damage than the Hiroshima bomb combined with the one dropped on the city of Nagasaki three days later, he added.

Japan is the only country to have come under nuclear attack, and uses the "never again" mantra to come to terms with the impact of the two bombs dropped in August 1945.

Article 5 of the country’s constitution renounces war, and states that “land, sea, and air forces, as well as other war potential, will never be maintained".

But when asked whether Japan should acquire the means to strike North Korean missile sites, Mr Abe did not reject the idea of a pre-emptive strike.

Japan currently relies on allies such as the US for nuclear deterrence, and refused to ratify or negotiate a landmark UN Treaty on the Prohibition of Nuclear Weapons last month.