Secretary of State John Kerry took his “Plan B” to the Senate Committee on Foreign Relations on Wednesday. He said a proposed “safe zone” in Syria would require between 15,000 and 30,000 US troops.

“Our Pentagon estimates that to have a true safe zone in the north of the country you may have upwards of fifteen to thirty thousand troops. Now are we ready to authorize that? Are we ready to put them on the ground?” Kerry said.

The Obama administration previously discounted the idea of establishing a safe zone. On July 23 retired U.S. general John Allen said an “air exclusion zone” inside Syria was not “part of the conversation” with Turkey during negotiations allowing US planes to use the Incirlik Air Base in Turkey to conduct airstrikes in Syria and Iraq.

Following Allen’s remarks the establishment media in the United States reported the US had reached an agreement with Turkey on a safe zone. Reports included maps showing areas along the Turkish border where the zone would be declared to protect civilians from the Syrian government, according to Bloomberg.

In December Turkish President Recep Tayyip Erdogan provided details on a plan for a safe zone. During an interview with Al Arabiya TV Erdogan said the zone would reach 25 kilometers inside Syria and stretch 98 kilometers along the border with Turkey. He said Syrian refugees currently in Turkey would be transferred to the area.

Erdogan and the Turks attempted to sell the idea as an “ISIS-free zone” despite repeated allegations and evidence Turkey supports the Islamic State and provides safe passage for jihadists over the border.

Turkey renewed its call for a safe zone in mid-February.

Political Class Supports Safe Zone

A number of politicians have called for a safe zone in Syria, including presidential frontrunner Donald Trump.

“What I like is build a safe zone in Syria. Build a big, beautiful safe zone, and you have whatever it is so people can live, and they’ll be happier,” Trump said during a rally held in Knoxville, Tennessee in November.

Republican presidential candidate Marco Rubio also expressed his support.

“We’re doing nothing to help those people on the ground, which is why I’ve said we need to create a safe zone in Syria, with the cooperation of our allies. And that will address three points: Number 1, allowing a non-radical-jihadist group to organize and prepare themselves. Number 2, to stem some of this flow of migrants that are leaving the region and going into Europe. If they had a place they could stay safely, they wouldn’t make that journey. And number 3, to ultimately have something in place for a future without Assad,” Rubio told Fox News in October.

“I don’t think it’s in the Russians’ interest to engage in an armed conflict with the United States,” Rubio told CNBC’s John Harwood when asked if a no-fly zone would risk confrontation with Russia.

Hillary Clinton voiced support for the plan in October. “I personally would be advocating now for a no-fly zone and humanitarian corridors to try to stop the carnage on the ground and from the air,” Clinton said.

German Chancellor Angela Merkel said earlier this month she supports the idea. “In the current situation, it would be helpful if there was an area there in which none of the warring parties carry out attacks by air—so a type of no-fly zone,” she told the Stuttgarter Zeitung newspaper. Merkel had previously rejected a proposed safe zone.

Vice Chairman of the Joint Chiefs of Staff Paul Selva, however, told the Senate Armed Services Committee establishing a safe or no-fly zone would risk confrontation with Russia.

John McCain, who also supports a no-fly zone, criticized Selva following his remarks. He said it was “one of the most embarrassing statements he’s ever heard from a uniformed military officer.”