* Most Gulf states fear deal will embolden Iran

* Iran's Zarif urges them to help combat instability

* Discussions also cover Syria, Islamic State

(Adds Zarif article)

By David Brunnstrom and Noah Browning

DOHA, Aug 3 (Reuters) - U.S. Secretary of State John Kerry began talks with Gulf states in Qatar on Monday, seeking to convince them of the merits of last month's nuclear deal with Iran and to discuss the battle against Islamic State militants and the war in Syria.

Most Gulf Arab states are worried that Iran's July 14 accord with the United States and other powers will hasten detente between Tehran and Washington and embolden the Islamic republic to support paramilitary allies in the region.

Last month, world powers agreed to lift sanctions on Iran in return for curbs on nuclear work the West suspects was aimed at making an atomic bomb but Tehran says is peaceful.

Speaking in Egypt on Sunday, Kerry said the United States had labelled Iran the world's number-one state sponsor of terror, but this was precisely why it was so important to ensure Tehran did not obtain a nuclear weapon.

"There can be absolutely no question that if the Vienna plan is fully implemented, it will make Egypt and all the countries of this region safer than they otherwise would be or were," he said, adding that he would discuss ways to ensure the future security of the region in Doha.

In Doha, Kerry will meet members of the Gulf Cooperation Council, which groups Saudi Arabia, the United Arab Emirates, Bahrain, Kuwait, Oman and Qatar.

He will also hold trilateral talks with Russian counterpart Sergei Lavrov and Saudi Arabia's Foreign Minister Adel al-Jubeir, which U.S. officials say will focus on the war in Syria.

Russia has been trying to bring about rapprochement between the Syrian government and regional states including Saudi Arabia and Turkey, to forge an alliance to fight Islamic State.

Kerry said last month he planned to discuss with Lavrov combating Islamic State militants and the role Iran could play.



IRANIAN ROLE

Iran's Foreign Minister Mohammad Javad Zarif wrote an article in several Arab newspapers to coincide with the talks, urging Gulf Arab countries to work with Iran to combat a wave on instability in the Middle East.

"We must all accept the fact that the era of zero-sum games is over, and we all win or lose together," he wrote in Arabic, backing up his statement with passages from the Koran.

Nonetheless, Iran remains locked in a struggle with Saudi Arabia and its allies for regional primacy. A deadly bombing in Bahrain last week, which the government linked to Iran, was taken by many as a sign Tehran could not be trusted.

U.S. officials say Kerry's diplomatic outreach in Doha is a follow-up to a summit with Gulf Arab leaders called by President Barack Obama at Camp David in May, which was snubbed by the leaders of Bahrain and Saudi Arabia.

At that meeting Obama responded to worries among Gulf states about the Iran deal by vowing to back them against any "external attack". Obama stopped short of offering a formal defence treaty that some Gulf states wanted. Instead he announced more modest measures, including integrating ballistic missile defense systems and beefing up cyber and maritime security.

On Wednesday, the U.S. State Department approved the sale of 600 Patriot anti-missile missiles to Saudi Arabia at an expected cost of $5.4 billion as well as $500 million worth of ammunition for various weapons systems.

(Reporting by David Brunnstrom, Editing by William Maclean and Andrew Heavens) ((david.brunnstrom@thomsonreuters.com; +1-202 354 5835; Twitter: @davidbrunnstrom; Reuters Messaging: david.brunnstrom@thomsonreuters.com@thomsonreuters.net))