NASHVILLE, Tenn., Nov 13 (Reuters) - U.S. Secretary of State Condoleezza Rice on Tuesday accused Iran of spreading "violent extremism" across the Middle East and said a strong Palestinian state could act as a bulwark against this threat.

Speaking to American Jewish leaders at a conference in Nashville, Tennessee, Rice reassured them of Washington's commitment to protect longtime ally Israel against threats from Tehran and said successful Palestinian statehood negotiations could counter Iran's power in the region.

"We will defend against any action, as we always have, that would compromise Israel's security," Rice said to applause from delegates at the meeting of the United Jewish Communities.

The United States is hosting a peace conference in Annapolis, Maryland, probably this month, that Rice hopes will kick-start serious talks between Israelis and Palestinians on core issues -- the right of return of refugees, the future of Jerusalem and the contours of a future Palestinian state.

Rice said a strong Palestinian state, where Israel's security was assured, would counter a rise of extremism across the region that was being spurred on by Iran's actions.

"A responsible Palestinian state can be a bulwark against that threat (of extremism)," said Rice. "This makes the two-state solution more urgent than ever," she added.

The United States is seeking support from skeptical Arab states such as Saudi Arabia at the Annapolis conference and Rice said "responsible" Arab nations must demonstrate they believed Israel had a permanent home in the Middle East.

"The time has come to seize that opportunity and that is why we intend to hold a serious and substantive meeting in Annapolis," Rice said, without providing details.

Rice, who returned from the region last week, urged both sides to make painful sacrifices and difficult choices they needed for peace, saying the future of the entire Middle East was at stake.

Both sides are seeking to draft a joint document ahead of the meeting but have so far been unable to bridge their differences and agree on a text, which diplomats say will likely be short on specifics.

'RISING EXTREMISM'

Rice has argued more strongly in recently weeks that success in resolving the Israeli-Palestinian issue will help counter what Washington sees as a growing threat from Iran on both its nuclear program and in backing groups such as Hezbollah in Lebanon and Hamas in the Palestinian Territories.

"In the rise of an aggressive Iranian regime, we see that violent extremism is evolving in new and dangerous ways -- ways that make it a threat not only to the people of one nation or one race or one religion but to everyone in the Middle East," said Rice.

"Increasingly the government of Iran is putting itself at the head of this violent extremism rising," she added.

The United States is spearheading a diplomatic campaign against Iran over its nuclear program, which the West believes is aimed at building a bomb and Tehran says is for power generation.

Washington is pushing the U.N. Security Council to impose a third round of sanctions against Iran, and Washington last month slapped restrictions on the Iranian Revolutionary Guard Corps as well as its elite Qods force.

"These sanctions help provide the teeth that our diplomacy needs to succeed," said Rice, repeating that all options, including the military one, remained on the table.

"The United States will continue to rally responsible nations everywhere to confront the dangerous policies of the dangerous Iranian government," she said. (Writing by Sue Pleming; Editing by Eric Beech)

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