Kolkata, May 7 (IANS): Calling nuclear-armed Iran a principal threat to the world, US Secretary of State Hillary Clinton Monday said proliferation of nuclear weapons is one of the biggest problems in the world.

"The proliferation of nuclear weapons is one of the biggest problems the world is facing. It's not only one country that we worry about, we worry about nuclear weapons proliferation in other countries too," she said at a gathering in La Martiniere school for girls here on the second day of her India visit.

"A nuclear arms race - that would be very damaging… our biggest fear is that nuclear weapons could fall into the hands of terrorist groups."

"We believe that at this moment the principal threat is nuclear-armed Iran because Iran is a state sponsor of terrorism. They work through a proxy called Hizbullah. Recently we broke a plot where the Iranian government was trying to murder the Saudi ambassador to the US," she said.

"Recently they were engaged in bomb building in Thailand. So I just want everybody in India to understand that we have nothing against Iranian people. President Obama has said we want a different relationship with Iranian people but so far there has been no reciprocity. And what we hear from the region surrounding Iran is a lot of anxiety, what they believe is that nuclear-armed Iran is a threat to world peace."

When asked why the US administration has stopped short of taking any action against Israel as it has violated several UN resolutions, Clinton said: "Obviously the US believes that whatever difference one might have with the situation in Middle East, Israel has been defending itself for 60 years and has left no stone unturned to bring a peaceful resolution to the situation, but it has so far been unsuccessful in doing so."

"We continue to press for peaceful resolution, particularly on Palestinian issues, which the US cares about," she said.