Kerry made the comments on Wednesday while discussing the years-long Syrian conflict with the Senate Committee on Foreign Relations.
He told the panel that creating a safe zone is not as simple as it sounds, because aside from shielding the airspace, a large group of soldiers are also required to protect people from Daesh (ISIL) attacks.
Syria Safe Zone Wants 30,000 Troops: Kerry
“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, referring to an estimate the Pentagon had made several months ago.
Earlier, the top US diplomat warned that if the Syrian ceasefire deal that the US and Russia agreed to on Monday falters, Washington will resort to its Plan B options.
In response, Russian Foreign Minister Sergei Lavrov dismissed the remarks on Thursday, saying there are no alternative plans.
Syrian President Bashar al-Assad also agreed to the deal, saying he is ready for a ceasefire in case the terrorists did not use it to advance their ambitions and that the countries backing them pull their support.
Russia has been conducting an aerial campaign against Daesh positions in Syria since September last year, upon a request from Damascus.
President Barack Obama’s administration had previously set forth the idea of establishing a safe zone in northern Syria with help from Turkey.
In November last year, the Wall Street Journal reported that Washington was pressing Ankara to seal its border with Syria by deploying more troops to the area.
Turkish President Recep Tayyip Erdogan laid down in December the details of a proposed zone, reaching 25 kilometers inside the Arab country and stretching 98 kilometers along the border with Turkey.
US Defense Secretary Ashton Carter says that to enforce an area of that size a “substantial” ground force would be needed.
Nearly five years of turmoil has claimed the lives of more than 270,000 people in Syria and displaced millions, according to the so-called Syrian Observatory for Human Rights. Some reports, however, put the death toll as high as 470,000.
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