U.S. President Donald Trump's order to withdraw all 2,000 US troops from Syria has drawn criticism from both his cabinet and U.S. allies. 

The opposition voices are coming from everywhere. The most fierce reaction came from Defense Secretary Jim Mattis who will leave his position on January 1. 

Mattis emphasized in a parting letter that he believes the U.S. derives its strength from its relationships with allies and should treat them with respect, and the country must also be "clear-eyed" about threats, including the Islamic State militants. 

He wrote that the president deserves someone atop the Pentagon "better aligned" with him, suggesting both of them weren't on the same page. 

Trump appeared to have realized this. Earlier this week his acting chief of staff said Trump had known for "quite some time now" that he and Mattis "did not share some of the same philosophies". 

Senate Majority Leader Mitch McConnell said Trump needs to reconsider pulling American troops out of Syria. In a letter with other Republicans, he wrote: "We believe that such action at this time is a premature and costly mistake that not only threatens the safety and security of the United States but also emboldens the Islamic State group, President Bashar Assad's government, Iran and Russia." 

In the letter, the Republicans have asked Trump to wait 90 days before making a decision. 

Key members of the anti-ISIL coalition, including France, Britain, and Germany, also reacted with skepticism, saying that much remains to be done in Syria. 

France said it will remain in Syria because the fight against terrorism is not over. A British government statement warned that "even without territory, IS (ISIL) will remain a threat". Germany also voiced concern, saying in a statement that "the abrupt change of course by the American side comes as a surprise".