U.N. Secretary General Antonio Guterres said Wednesday that his determination to work toward creating a world free of nuclear weapons was renewed by his recent trip to Nagasaki, one of the two atomic-bombed cities in Japan.

"Last month, I had the extraordinary honor of visiting Nagasaki to commemorate the seventy-third anniversary of the atomic bombing," Guterres said at a high-level U.N. General Assembly meeting to commemorate the International Day for the Total Elimination of Nuclear Weapons.

(Japanese Prime Minister Shinzo Abe (L) Guterres shake hands in New York on Sept. 25)

"The reality of the death and destruction caused by only one nuclear weapon -- small by today's standards -- reinforced my personal commitment to achieving a world free of nuclear weapons," he said.

Guterres traveled to Nagasaki in August, becoming the first sitting U.N. chief to attend an annual memorial ceremony to mark the 1945 U.S. atomic bombing of the southwestern Japanese city.

In May, Guterres unveiled his disarmament agenda, which recognizes that progress toward the goal of a nuclear-free world remains uneven.

"That is why I have called for the resumption of sincere, substantive and results-oriented dialogue towards the total elimination of nuclear weapons, as well as the implementation of existing commitments," he said, adding that countries possessing nuclear weapons have a responsibility to lead.

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Guterres pressed the United States and Russia to re-engage in the dialogue necessary to maintain their track record of bilateral arsenal reductions.

He also reiterated that all countries have responsibilities in the pursuit of nuclear disarmament, mainly the fulfilment of their nonproliferation obligations.

Saying it is now time to make "tangible progress to rid our world of nuclear weapons," the U.N. chief pledged both his own personal support and that of the U.N. system for efforts toward nuclear disarmament.

"Such a challenging goal will not be achieved overnight. But we must take urgent steps now," he said.

Also Wednesday, four more countries added their names at a U.N. ceremony to the list of nations that have ratified the world's first nuclear weapons ban treaty together with seven other nations that have newly signed onto the pact.

Officially known as the Treaty on the Prohibition of Nuclear Weapons, the document was ratified by Gambia, Samoa, San Marino and Vanuatu.

The seven countries that added their signatures to the accord are Antigua and Barbuda, Benin, Brunei, East Timor, Guinea-Bissau, Myanmar and the Seychelles.

The treaty was adopted in July last year. A total of 50 countries must both sign and ratify the treaty before it can enter into force. With the new additions, a total of 19 nations have now ratified it and 67 others have signed onto it.