Kerry was to spend several hours in the western city of Jeddah consulting with the leadership of the oil-rich Sunni Muslim monarchy, which has been outspoken in its opposition to Syrian President Bashar al-Assad.
President Barack Obama is cautious about deeper US involvement in the increasingly sectarian conflict but has vowed to step up support for the rebels after concluding that Assad defied warnings and used chemical weapons.
US policymakers have privately voiced concern that Saudi Arabia and fellow monarchy Qatar could increasingly embrace hardline Sunni guerrillas in strategically placed Syria if Western powers leave a vacuum.
In interviews ahead of his departure to Jeddah, Kerry declined to raise concerns about potential Saudi and Qatari support for hardliners but said it was critical to strengthen moderate rebels to prevent an Assad victory.
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"If the United States does nothing, and the rest of the world does nothing, then Syria is going to wind up in an even worse condition than it is today," Kerry told CBS News from New Delhi.
Saudi Arabia, while a longstanding US ally, practises a puritanical form of Wahhabi Islam. US officials have in the past voiced concern about money from Gulf Arabs funding Sunni hardliners in Afghanistan, Pakistan and elsewhere.
Assad, who leads a secular state, belongs to the heterodox Alawite sect which some Sunni conservatives consider un-Islamic. Assad enjoys strong support from Iran, a Shiite Muslim state which counts Syria as its main Arab ally.
Kerry has insisted that the United States is not looking necessarily for a victory by the rebels but instead wants to step up pressure on Assad until he agrees to peace negotiations as set out by a conference in Geneva last year.
Russia, a supporter of the Assad family's four-decade rule in Syria, joined the United States in backing the Geneva plan.