Florida Republican Sen. Marco Rubio said on Tuesday that war with Iran is ultimately in the hands of the country's Supreme Leader Ayatollah Ali Khamenei.

"It's all on them, and it's a grave risk," Rubio, a member of the Senate Foreign Relations Committee, said on CNBC's "Squawk Alley." "I don't want a war, we don't want a war, but that's up to them."

Rubio's comments come as the American military is reportedly reviewing plans to send as many as 120,000 troops to the Middle East in the event that Iran attacks U.S. forces. President Donald Trump disputed those reports earlier in the day but said he would send "a hell of a lot more troops than that" if necessary.

The U.S. and Iran are locked in a dispute over American presence in the region and allegations that Iran is stirring up conflict via proxy groups. The U.S. has also reinstated sanctions on the country as part of a "maximum pressure campaign" designed to curb Iranian military activity. Some sanctions had been lifted under the terms of President Barack Obama's nuclear deal with the country. Trump withdrew the U.S. from that agreement in 2018.

The Trump administration in recent weeks has announced the deployment of military equipment to the region, including the USS Abraham Lincoln carrier strike group and a U.S. Air Force bomber task force sent in response to what the administration characterized as "heightened Iranian readiness to conduct offensive operations."

Rubio said he hoped war would be avoided, but that Trump could not ignore intelligence assessments he said showed that Iran had ordered strikes against American personnel and interests.

"Again, I'm not cheering for this, I don't want this to happen, but there is no way the president of the United States can ignore clear movements on the ground coupled with clear intelligence that indicates that Iran is moving towards, or has, in many cases, ordered strikes against U.S. personnel and U.S. interests in the region," Rubio said.

"They are doing absolutely the right thing," Rubio said, referring to the Trump administration. "And the question of whether or not there is an armed conflict, that is now in the hands of the [Islamic Revolutionary Guard Corps], of General [Qassem] Soleimani, and ultimately of the ayatollah and of Iran."

The White House has faced criticism that it is saber rattling in the Middle East and attempting to provoke Iran into a military conflict.

Iran's ambassador to the United Kingdom said Tuesday that the United States is playing a "very dangerous game" that could "drag Iran into an unnecessary war," according to USA Today. And Trita Parsi, the founder of the National Iranian American Council, wrote in a post on Twitter that "this is a TOTALLY UNNECESSARY crisis!"

"We're only here cuz Trump quit the deal and put Bolton in charge of Iran policy!" he wrote, referring to National Security Advisor John Bolton, who advocated for a preventive strike against the country before he joined the Trump administration.