Speaking to Army Radio on a visit to Israel, the Republican senator deflected concerns that weapons provided to rebels could fall into the hands of terrorists, who might use them against the United States and Israel.
"There's [sic] no good options," said McCain, "Would you rather have these weapons - perhaps some of them - in the hands of the wrong people, or would you rather have [Syrian President] Bashar Assad prevail and then encourage Iran to further their ambitions on nuclear weapons?"
Joining McCain in the interview was fellow Republican Sen. Lindsey Graham, who criticized the Obama administration's hesitation in acting on threats to Assad over his use of chemical weapons.
"When you say to a leader of another country, 'You can't cross this line,' and that person does and nothing happens, it's not good. The Iranians need to believe that America's serious about stopping their nuclear program. I think our policies in Syria are sending a mixed message," Graham told Army Radio.
With Russia and Iran arming Assad's forces, and Lebanon's Hezbollah fighters joining the war on his behalf, Western powers have agreed to step up aid to the mainly Sunni rebels.
McCain also addressed the peace negotiations that U.S. Secretary of State John Kerry is trying to re-launch between Israel and the Palestinians, showing he sides with Prime Minister Benjamin Netanyahu's approach: that talks should only start without preconditions.
"There should be no preconditions," McCain told Army Radio, "I don't know if that pressures Abbas or pressures Netanyahu, but I think that it's very legitimate to say that the two parties should sit down across the table from each other with no preconditions. That's the only way I think that it can succeed."
The Republican also said that while he hopes Kerry will succeed in his efforts to get the two sides to talk, he doesn't believe the public should get its hopes up. "To raise expectations too high would be a mistake," he said.
Saudi Arabia urges EU to arm rebels
Meanwhile, Saudi Arabia, a foe of Assad, has urged the European Union to arm Syrian rebels without delay, following the United States' lead.
The European Union lifted restrictions on arming the rebels in May when it failed to renew a weapons arms embargo before it expired on June 1. But Britain and France, which had advocated lifting the ban, said they would not send weapons before August 1.
"The Syrian opposition is not only fighting an illegitimate regime, but also fighting a foreign occupier," Saudi state news agency SPA quoted Foreign Minister Prince Saud al-Faisal as telling an EU-GCC ministerial meeting in Bahrain on Sunday.
He was referring to Iranian-backed Lebanese Hezbollah forces that have joined in recent fighting alongside Assad's military, notably spearheading the capture of the border town of Qusair.
Saudi Arabia and Qatar have been the most active Arab nations in backing the mostly Sunni Muslim Syrian rebels.
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