U.S. Democratic presidential candidate Senator Barack Obama (D-IL) smiles before his meeting with Israel's Foreign Minister Tzipi Livni (not pictured) in Jerusalem July 23, 2008. Obama pledged staunch support for Israel on Wednesday in Jerusalem, describing the Jewish state as a miracle and holding only a low-profile meeting with Palestinian leaders. REUTERS/Ronen Zvulun

SDEROT, Israel (Reuters) - U.S. Democratic presidential candidate Barack Obama said on Wednesday a nuclear Iran would pose a “grave threat” and that the world must stop Tehran from obtaining an atomic weapon.

Obama told reporters during a visit to Israel that if elected, he would take “no options off the table” in dealing with the Iran issue and said tougher sanctions could be imposed.

“A nuclear Iran would pose a grave threat and the world must prevent Iran from obtaining a nuclear weapon,” Obama told reporters after visiting the Israeli town of Sderot, which lies close to the border with the Hamas-run Gaza Strip.

He said the international community should immediately offer “big sticks and big carrots” to persuade Iran to halt its nuclear program. The West suspects Iran wants to build atom bombs but the Islamic Republic says its aims are peaceful.

“Iranians need to understand that whether it’s the Bush administration or the Obama administration, this is a paramount concern to the United States,” he said in Sderot, which has been hit by cross-border rockets fired by Gaza-based militants.

Israel says Iran provides funds and weapons to Hamas.

“I think there are opportunities for us to mobilize a much more serious regime of sanctions on Iran, but also to offer them the possibility of improved relations to the international community if they stand down on these nuclear weapons.”