US Secretary of State John Kerry arrived in Saudi Arabia on Tuesday in hopes of coordinating support for Syria's rebels amid fears that a prolonged civil war will embolden extremists.
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.
Kerry told a conference of major powers in Qatar on Saturday that the United States and its partners were boosting military aid to Syria's mainstream rebels, although he has been reticent on the exact nature of the assistance.
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.
"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.
A worse scenario in Syria could include "a total breakup, with radicals, extremists able to get a hold of chemical weapons and free to use it as a base to begin to conduct their operations again against the West and the United States," Kerry said.
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 Shia Muslim state which counts Syria as its main Arab ally.
Kerry has called for greater support to Syria's rebels by accusing Iran of "internationalisation" of the conflict through the growing role in the war of guerrillas from Hezbollah, a Lebanese Shiite movement backed by Tehran.
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.
While the United States has hailed the stance as cooperation by Russia, Kerry's trip comes amid a showdown as Washington demands Moscow turn over former US security contractor Edward Snowden who is wanted for exposing vast US surveillance operations.
Snowden fled Hong Kong to Russia in hopes of reaching a friendly Latin American nation but he then mysteriously disappeared.
But Russia on Tuesday denied that Snowden had ever crossed its border and slammed US claims of complicity.
Kerry will meet in Jeddah with Saudi Foreign Minister Prince Saud al-Faisal as well as Prince Bandar bin Sultan, the kingdom's intelligence chief who was formerly ambassador to the United States.
Kerry will head later Tuesday to Kuwait, another US-allied monarchy, and then this week will go to Jordan in a new bid at making peace between Israel and the Palestinians.
He was returning to the region after three days in India, where he pledged to work toward stronger ties between the world's two largest democracies and promised to respect New Delhi's concerns over any US reconciliation with Afghanistan's Taliban.