Under the reported plan, about 7,000 American troops would start going home in January, and the rest would exit in the coming months in a phased drawdown. McGurk also cited gains in accelerating the campaign against IS, but that the work was not yet done.
The resignation of Jim Mattis as United States defence secretary is ringing alarm bells throughout the West.
Earlier this month, McGurk reportedly stated it would be "reckless" to believe that Daesh was defeated, and therefore, United States forces must stay in the country in order to oppose terrorists. He chose to speed up his plan to leave in mid-February.
The Associated Press, which first reported McGurk's resignation, reported that he said in a resignation letter to Secretary of State Mike Pompeo that ISIS was on the run, but wasn't yet defeated and that USA work in Syria wasn't yet done.
The officials spoke on condition of anonymity to discuss internal deliberations.
McGurk submitted his resignation on Friday, just one day after Defense Secretary James Mattis quit his post citing fundamental disagreements with the commander-in-chief - including one over the importance of honoring US alliances.
On Thursday, Trump announced that Mattis was retiring in February.
The US has about 14,000 troops in Afghanistan working either with a North Atlantic Treaty Organisation mission to support Afghan forces or in separate counter-terrorism operations. The final decision on when the troops will be out is not yet confirmed, though one official claimed that they will come back by summer.
A withdrawal of USA troops may force a reckoning within the Afghan government, which was reportedly caught unawares by the announcement. Senator Lindsey Graham, who used to support the president on many issues, even said that the only reason "they weren't dancing in Tehran and ISIS camps is that they just don't believe in dancing".
With the insurgents in control of large stretches of the country and chronically understrength Afghan forces suffering thousands of casualties a month, even a partial USA withdrawal could reduce the incentive of the Taliban to strike a deal and erode the willingness of Afghan troops to fight. Many of these individuals have significantly benefited from the war and from USA support.
McGurk, 45, previously served as a deputy assistant secretary of state for Iraq and Iran. The president's announcement also drew sharp criticisms from congressional Republicans, such as US Senator Lindsay Graham.
Jim Jeffrey, a veteran diplomat who was appointed special representative for Syria engagement in August, is expected to stay in his position, officials said. The Taliban has steadily gained ground, controlling large chunks of the Afghan countryside and threatening to overrun major provincial capitals as the Afghan military and police suffer increasing casualties and attrition.
The SDF, a Kurdish-led force that is America's only military partner in Syria, said Thursday: "The war against Islamic State has not ended and the group has not been defeated".