New York, April 28 (RHC)-- U.S. Secretary of State John Kerry and Iran's Foreign Minister Mohammad Javad Zarif have met on the sidelines of a UN anti-nuclear weapons conference in New York. The meeting was held on Monday at the residence of Iran's ambassador to the United Nations where the two are taking part in the 2015 Review Conference of the Parties to the Treaty on the Non-Proliferation of Nuclear Weapons (NPT).

It was the first time that the top Iranian and U.S. diplomats met since April 2nd, when the six countries of the P5+1 -- the United States, Russia, China, France, Britain, and Germany-- reached a mutual understanding over the Islamic Republic's nuclear program.

Zarif and Kerry did not speak to reporters as the meeting started, but earlier in the day Kerry defended nuclear talks with Iran in his address to the summit. The global community is "closer than ever" to a "good comprehensive" agreement with Iran, he said, adding, however: "The hard work is far from over and some key issues remain unresolved."

Addressing the conference on Monday, Zarif, who was speaking on behalf of the Non-Aligned Movement (NAM), said, "We firmly believe that any use or threat of use of nuclear weapons would be a crime against humanity and a violation of the principles of the Charter of the United Nations and international law, in particular, international humanitarian law."