The U.S. military began the process of withdrawing its troops from Syria following a drawdown ordered by President Donald Trump, a military official said Friday.

Col. Sean Ryan, a spokesman for the U.S.-coalition fighting the Islamic State group in Syria and Iraq, declined to discuss specific operational details of the pullout such as timings and troop movements, but said in an email the withdrawal was underway.

About 2,000 U.S. troops are in Syria.

The military has moved some cargo from Syria already, according to a U.S. Defense official who was not authorized to speak publicly about the matter. Trump's order is for a complete withdrawal of troops and their equipment.

The troops in Syria have weapons, communication equipment and vehicles that will need to be moved. Planning is underway to identify facilities that can handle the equipment, the official said. No troops have left yet.

It could take months to complete the withdrawal.

The development comes as White House national security adviser John Bolton appeared to contradict Trump's order when he said the withdrawal would not be immediate, it would not happen before ISIS is fully defeated and it would be contingent on a pledge by Turkey not to attack the U.S.'s Kurdish military allies in Syria.

None of Bolton's conditions have been met.

President Recep Tayyip Erdogan refused to meet with Bolton during his visit to Turkey this week and described his conditions for the U.S. troop drawdown as a "grave mistake." Turkey considers some members of a Syrian-Kurdish Arab coalition fighting ISIS alongside U.S. troops to be terrorists and has applauded Trump's decision.

Turkey has amassed thousands of troops along its border with Syria and has long threatened to unilaterally attack Kurdish militias who it claims has ties to separatist groups who have carried out assassinations and bombings against the Turkish government for decades. The U.S. withdrawal from the area could embolden Ankara.

"I have some concerns, my greatest concern…probably is the Kurds and… just how defenseless we are going to leave them," newly elected Sen. Kevin Cramer, R-N.D, told Stars and Stripes, an American military newspaper.

On Monday, Bolton said Trump would "not allow Turkey to kill the Kurds."

Trump announced the withdrawal about three weeks ago on Dec. 19. A day later, Defense Secretary Jim Mattis released a resignation letter in which he indicated that he no longer agreed with the president's thinking on military operations.

According to a recent report by the Center for Strategic and International Studies, ISIS is far from obliterated. The Washington-based think tank estimates 20,000 to 30,000 Islamic State militants may still be in Syria and Iraq.

The Syrian Observatory for Human Rights, a Britain-based group that monitors the Syria conflict via a network of activists on the ground, said the U.S. withdrawal began Thursday night. It said a convoy of about 10 armored vehicles, in addition to some trucks, pulled out from a military base in Syria’s northeastern town of Rmelan into Iraq.

The U.S.-led coalition has been fighting ISIS in the Middle East since 2014 and Mattis said before leaving his job that declaring victory and leaving Syria would be a mistake.

Secretary of State Mike Pompeo has been defending Trump's order this week while on a tour of the Middle East where he has been rebuking former President Barack Obama's policies for the region. In a speech in Cairo, he said Trump "made the right decision to bring our troops home from Syria" and the U.S. is "committed to the complete dismantling of the ISIS threat and the ongoing fight against radical Islamism."

But Pompeo also caused confusion about Washington's Syria policy. He said in his speech in Cairo that Obama was wrong to withdraw U.S. troops from Iraq.

"When America retreats, chaos follows. When we neglect our friends, resentment builds. And when we partner with enemies, they advance," Pompeo said.

Less than 24 hours later, U.S. troops started pulling out of Syria.

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