Democratic presidential aspirant Barack Obama has warned that a nuclear-armed Iran would pose a "grave threat" to the world.

Mr Obama made the comments during his visit to Israel today, as he seeks to win over the wavering Jewish vote back home in the United States.

The presumptive nominee, who will take on Republican rival John McCain this autumn, is visiting Israel on a diplomatic trip to the Middle East and Europe which has also seen him visit Iraq, Jordan and Afghanistan.

Today he visited the town of Sderot which has suffered under a hail of missiles fired from the Hamas-controlled Gaza Strip in recent months.

And the Illinois senator pledged his "unshakeable commitment" to Israeli security and the Middle East peace talks.

On Iran, Mr Obama declared: "A nuclear Iran would pose a grave threat and the world must prevent Iran from obtaining a nuclear weapon."

Earlier, the Democrat held talks with Palestinian president Mahmoud Abbas in Ramallah where he claimed he would quickly engage in the Middle East peace talks if elected the next US president.

Mr Obama has previously been at pains to back Israel and in a speech last month emphasised his commitment to working towards a two-state solution "living side by side in peace and security".

A statement to reporters issued before his visit to Israel, only his second ever, said: "Israel is a strong and close friend of the United States, and is confronting grave threats from Gaza to Tehran."

His Republican rival Mr McCain has made clear he will also act to ensure Iran does not develop nuclear weapons. Speaking from the US on the eve of Mr Obama's trip, he said: "I have to look you in the eye and tell you that the United States of America can never allow a second Holocaust."
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