"The Iranians have to understand that if they keep using the negotiations to gain time to complete a nuclear program then the situation will become extremely dangerous," he said.
"The consequences of an Iranian nuclear program is that other countries in the area will also want nuclear weapons," and when nuclear weapons become "almost conventional," "we would face a nuclear war at some point, which would be a turning point in world history," he said.
Iran and the West are locked in a bitter dispute over the former's nuclear ambitions. The West accuses Tehran of developing nuclear weapon under the cover of peaceful nuclear program, a charge Iran has consistently denied.
On the Syria crisis, Kissinger said there was no easy solution.
The world would face "a huge human tragedy" if it stands on the sidelines and does not intervene, but "if it does intervene, it will be in middle of vast ethnic conflict."
However, the current conflict in Syria can be resolved if the United States and Russia were to sponsor an agreement that other countries would also back, he said.
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