A senior administration official says President Trump "thought he got a commitment" from the Turkish president to protect the fighters.
Patrick Shanahan will take over as acting secretary to cover the accelerated departure.
Speaking on condition of anonymity, officials reveal the president took action without consulting his allies or national security team.
The clergyman—whose detention in Turkey generated an outcry from evangelicals—had just returned to the U.S. after being held for nearly two years.
The area will be established by Oct. 15 and be 9 to 12 miles deep, with troops from Russia and NATO-member Turkey conducting coordinated patrols.
Iranian and Russian leaders support a military campaign to retake the last rebel-held stronghold in Syria as Turkey's president pleads for a cease-fire. U.S. and others warn of a bloody humanitarian disaster.
The tariffs on cars, alcohol and coal are unlikely to have much economic impact, but they highlight deteriorating relations with the U.S. and a feud that has helped trigger a currency crisis.
The president declares he will impose unspecified sanctions because Turkey has not freed an American it arrested in 2016. The announcement comes as the State Department holds a religious freedom event.
Unofficial election returns show him with enough votes to serve another term, one that carries new executive powers. Critics had warned about re-electing Erdogan, citing his increasingly autocratic tendencies.
The president holds individual conversations with French and British leaders. The White House says the three nations agreed the assault on Syria was "successful and necessary to deter" the future use of chemical weapons.