"Iran is seeking to obtain a nuclear weapon and constitutes the gravest threat to our existence since the war of independence," Mr Netanyahu said.
Referring to the Iranian-backed Hezbollah movement in south Lebanon, Mr Netanyahu said: "The terrorist forces of Iran threaten us from the north. For decades, Israel has not faced such formidable challenges.
"The responsibility we face is to achieve security for our country, peace with our neighbours and unity among us."
He spoke after the UN announced yesterday that Iran had enriched sufficient uranium to amass a nuclear bomb – a third more than previously thought. President Mahmoud Ahmadinejad of Iran has caused alarm in the West over its apparent threats to Israel and support for radical Islamist groups Hamas and Hezbollah.