Iran has enough radioactive material to produce four nuclear bombs, Israel's chief of military intelligence, General Aviv Kochavi, asserted at a security conference on Thursday.
"Today international intelligence agencies are in agreement with Israel that Iran has close to 100 kilograms (220 pounds) of uranium enriched to 20 percent, which is enough to produce four bombs," he told the annual Herzliya conference.
"Iran is very actively pursuing its efforts to develop its nuclear capacities, and we have evidence that they are seeking nuclear weapons," he said.
"We estimate they would need a year from when the order is given to produce a weapon."
Israel and much of the international community have long accused Iran of using its nuclear programme to mask a drive for weapons, a charge Tehran denies.
The Jewish state has pushed for tough sanctions against Iran and warned that it retains the option of a military strike if necessary to prevent Tehran from obtaining atomic weapons.
Israel has the Middle East's sole if undeclared nuclear arsenal, which international experts believe contains between 100 and 300 nuclear warheads, but it has never confirmed or denied such reports.
Earlier on Thursday, Defence Minister Ehud Barak praised new European sanctions against Iran's oil sector after talks with German Foreign Minister Guido Westerwelle, and called to expand sanctions to the financial system and central bank.
Later at the Herzliya conference, Barak said there was currently "broad international understanding that if the sanctions do not achieve their desired goal of stopping the Iranian nuclear military programme, the need to consider action will arise."
He also stressed the need for timely "action" against Iran, without specifying its nature.
"Many experts, not only in Israel but also in the world, believe that refraining from action would necessarily lead to a nuclear Iran, and that dealing with a nuclear Iran would be more complicated, more dangerous, and would cost more lives and money, than stopping it today," Barak said.
"Whoever says 'later,' might find that 'later' is too late," he warned.
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Speaking at the same conference, Strategic Affairs Minister Moshe Yaalon said Iranian nuclear facilities, believed to be underground and heavily reinforced, were not immune to attack.
"In my military experience, any site protected by humans can be penetrated by humans," said Yaalon, a former head of Israel's armed forces, in comments broadcast on Israeli public radio.
"At the end of the day all their sites can be hit."
"We argue that one way or another the Iranian military nuclear programme must be stopped," he added. "Such an unconventional regime must not have an unconventional (weapons) capability.
"A combination of tools are available to the West," Yaalon said. "That combination must include diplomatic isolation of the regime; the second tool is economic sanctions... and the last thing is a credible military option."
Yaalon also referred to an Iranian military facility rocked by a deadly explosion in November, claiming Iran had been developing a missile there intended to threaten the United States.
He said the site, at Bid Ganeh, near Tehran, was conducting research and development on a missile with a range of 10,000 kilometres (6,213 miles) at the time of the blast which killed at least 36 Revolutionary Guards.
It was "aimed at America, not us," a statement from the organisers of the Herzliya Conference quoted him as saying.
Iran's military said the explosion was the result of an accident.
The chief of staff of Iran's armed forces said at the time that the base was used in the production of "an experimental product" that would unleash "a strong fist in the face" of the United States and Israel.
Kochavi also warned on Thursday that Israel's enemies now command "some 200,000 rockets and missiles."
Intelligence estimates, he said, showed "one in every 10 houses in south Lebanon is a storage facility for missiles or rockets or a launch pad for devices that are increasingly accurate and destructive."
"From Lebanon, Syria and of course from Iran, they can hit the heart of our cities, and the whole region of Tel Aviv is within their reach," Kochavi said.