DOHA - US 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 Tehran to support paramilitary allies in the region.Last month, world powers agreed to lift sanctions on Iran in return for curbs on a nuclear program the West suspects was aimed at creating an atomic bomb, but which Tehran says is peaceful. Speaking in Egypt on Sunday, Kerry said the United States had labeled 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 a trilateral meeting with his Russian counterpart Sergei Lavrov and Saudi Arabia's Foreign Minister Adel al-Jubeir, which US 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 that with Lavrov he planned to discuss combating Islamic State militants and the role Iran could play.US 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 anxieties among Gulf states about the nuclear deal with Iran by vowing to back them against any "external attack" and pledging that the United States would consider using military force to defend them.Obama stopped short of offering a formal defense treaty that some Gulf countries had sought. Instead he announced more modest measures, including integrating ballistic missile defense systems and beefing up cyber and maritime security.On Wednesday, the US 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.