AMMAN - US Secretary of State John Kerry will press Arab leaders on Thursday to support President Barack Obama's plans for a new military campaign against Islamic State militants.In a strong measure of support, Saudi Arabia has agreed to host training camps for moderate Syrian rebels who are part of Obama's broad strategy to combat the militants, who have taken over a third of both Syria and Iraq, US officials said.The agreement, outlined by Obama's aides on the night of his speech to the American people laying out his expanded campaign against the Islamist group, appeared to reflect the depth of Saudi concern about Islamic State's threat to the region.Saudi Arabia, the richest Sunni Arab country, this year outlawed Islamic State as an extremist organization, but it is worried that the focus on the group will distract from what it sees as a bigger regional threat stemming from Shi'ite Iran.The conservative Islamic kingdom has long pressed the United States to take a bigger role in aiding moderate Syrian rebel groups, which it sees as the best hope of tackling both Islamic State and the regional ambitions of Tehran.