The United Nations marked the 25th anniversary of Chernobyl Tuesday by honoring the victims of the worst nuclear accident in history and stressing the need to do more to help communities in the affected areas of Belarus, Russia and Ukraine.

A man attends a vigil dedicated to firefighters and workers who died after the Chernobyl nuclear disaster at a service in the nearby northern Ukrainian city of Slavutych on Tuesday, when Belarus, Ukraine and Russia marked the 25th anniversary of the world's worst civil nuclear accident.?[Gleb Garanich / China Daily / Reuters]

More than 300,000 people were displaced and roughly six million were affected by the accident that took place at the Chernobyl nuclear power plant on 26 April 1986, which contaminated a swathe of territory half the size of Italy.

"The Chernobyl anniversary is an occasion both to remember the human cost of the disaster and to take stock of the many problems that still linger," Ambassador Maria Rubiales de Chamorro of Nicaragua, the Acting President of the General Assembly, said at a special commemorative meeting held by the 192-member body.

"But it is also a time to look ahead and seek solutions that hold promise for the affected communities and renew our commitment to a safer future," she added, noting that the affected communities require assistance in areas such as investments and socio-economic development.

Secretary-General Ban Ki-moon said that the anniversary is a time to remember the heroism of the firefighters and other emergency workers, as well as the plight of millions of people who were uprooted from the contaminated regions and those still living in the affected areas.

"Their sacrifices must never be forgotten; their suffering must never go unaddressed," he said in a statement to mark the anniversary.

He told the meeting of the Assembly that Chernobyl "cast a radioactive cloud across Europe and a shadow around the world," but it also highlighted international solidarity.

"Chernobyl was not a problem for Ukraine, Belarus or Russia alone. Chernobyl was our problem – a shared challenge for the world," said Ban, who last week became the first UN Secretary-General to visit the site of the disaster.

He added that the anniversary, as well as the accident at Japan's Fukushima Daiichi nuclear plant last month, calls for reflection and robust global debate on how to achieve the peaceful uses of nuclear energy and maximum safety.

Ban has outlined a five-step plan to enhance nuclear safety, beginning with "a top to bottom review" of current nuclear safety standards, both at the national and international levels. The plan also strengthening the work of the UN International Atomic Energy Agency (IAEA), putting a sharper focus on the nexus between natural disasters and nuclear safety, undertaking a cost-benefit analysis of nuclear energy, and building a stronger connection between nuclear safety and nuclear security.

"With the memory of Chernobyl and, now, the disaster in Fukushima, we must widen our lens," Ban wrote in an opinion piece published in the International Herald Tribune. "Henceforth, we must treat the issue of nuclear safety as seriously as we do nuclear weapons."

In a message to the opening of a photo exhibition in New York on the occasion of the anniversary, Ban pledged his determination to keep nuclear safety at the top of the international agenda.

"By working to ensure that nuclear power is used peacefully and safely, we can honor the memory of Chernobyl's victims and its lost heroes."

Ban will convene a high-level meeting on strengthening the international nuclear safety regime when world leaders gather at the UN in New York in September.