WATCH: John Kerry tells the Senate that Syria isn't like Iraq

A week after he made a forceful case for launching an attack on the regime of Syrian President Bashar al-Assad, Secretary of State John Kerry testified to the Senate Foreign Relations Committee that he would not rule out deploying soldiers in Syria if the conflict escalated.

"I don't want to take off the table an option that might or might not be on the table," said Kerry. However, he stressed that there was "zero capacity for boots on the ground" under the military campaign President Obama has proposed, which was crafted in response to Assad's alleged use of chemical weapons on civilians.

Kerry also said that the situation in Syria was nothing like the lead-up to the war in Iraq:

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Last week, Kerry said that U.S. intelligence had "high confidence" that Assad's regime used chemical weapons to kill 1,429 people in the Damascus suburb of Ghouta. Since the Syrian conflict began in 2011, more than 100,000 people have died as a result of the violence and more than 2 million Syrians have become refugees.

"This is not the time to be spectators to slaughter," Kerry said. "We have spoken up against unspeakable horror many times in the past; now, we must stand up and act."

On that point, Sen. Marco Rubio (R-Fla.), a potential presidential candidate in 2016, agreed.

"America can ignore these problems, but these problems won't ignore us," Rubio said. He added that not acting would "embolden Assad" and his allies in Iran, while telling "the rest of the world that there is no red line that they should fear crossing."

Membes of the committee questioned how effective a military strike would be, and whether Assad would eventually be succeeded by a government that is stable and democratic.

Kerry sounded very confident that an opposition group like the Al-Nusra Front, which has connections to al Qaeda, would not take power.

"The opposition has increasingly been defined more by its moderation, more by its breadth of membership," Kerry said.

Sen. John McCain (R-Ariz.), meanwhile, criticized Kerry for giving Assad's forces time to prepare by consulting with Congress, while Sen. Rand Paul (R-Ky.), who is opposed to any military intervention, said Obama should be allowed to launch strikes without Congress' permission. The opposing viewpoints represent the growing divide within the GOP between hawks and neo-isolationists.