The most senior U.S. military officer said that a letter appearing to announce an American troop withdrawal from Iraq was "a mistake" and should not have been sent to officials in Baghdad.

Gen. Mark Milley, chairman of the Joint Chiefs of Staff, said the letter from the top U.S. commander in Iraq was a poorly worded draft that was being worked on with the Iraqi government. "It was a mistake," he said, adding that U.S. troops were not pulling out.

Secretary of Defense Mark Esper said there had been "no decision whatsoever to leave Iraq." Confusion over the meaning and validity of the letter sent Pentagon officials scrambling. The letter from Marine Corps Brigadier Gen. William Seely to Iraq’s Ministry of Defense informed the Baghdad government of a “repositioning of forces over the course of the coming days and weeks to prepare for onward movement.”

The letter circulated one day after Iraq's parliament voted to expel American forces following the drone killing of Iranian Gen. Qassem Soleimani. The resolution was nonbinding, meaning it does not carry the force of law. It followed the death of Iranian Islamic Revolutionary Guard Corps leader Maj. Gen. Qassem Soleimani in a U.S. air strike near Baghdad International Airport on Sunday.

"Sir, in due deference to the sovereignty of the Republic of Iraq, and as requested by the Iraqi Parliament and the Prime Minister, CJTF-OIR will be repositioning forces over the course of the coming days and weeks to prepare for onward movement," Brig. Gen. William Seely, the top U.S. commander in Iraq, stated in an unsigned letter on Monday.

A number of news outlets vouched for the authenticity of the letter, as did an Army public affairs officer who posted and then deleted confirmation on Twitter.

The letter came after a vote on a resolution by the Iraqi parliament on Sunday to push U.S. forces out of Iraq. The resolution was nonbinding, meaning it does not carry the force of law. It followed the death of Iranian Islamic Revolutionary Guard Corps leader Maj. Gen. Qassem Soleimani in a U.S. air strike near Baghdad International Airport on Sunday.

The United States led an international invasion force on June 15, 2014, when President Barack Obama sent troops in response to offensives from the Islamic State of Iraq and the Levant (ISIL). Some 603 U.S. troops were killed in Iraq, according to Pentagon figures. Approximately 5,000 U.S. troops remain stationed there.