A Syrian boy watches as Turkish military vehicles, part of a US military convoy, take part in joint patrol in the Syrian village of al-Hashisha on the outskirts of Tal Abyad town along the border with Turkey, on October 4, 2019.Delil Souleiman | AFP | Getty ImagesTurkey has launched a military operation in northern Syria, Turkish President Recep Tayyip Erdogan said Wednesday, days after the Trump administration announced its controversial decision to pull U.S. troops out of the area.”Turkish Armed Forces together with the Syrian National Army against PKK / YPG and Daesh terrorist organizations in northern Syria #BarışPınarıHarekatı has started,” Erdogan wrote on Twitter, according to that site’s translation feature. “Our aim is to destroy the terror corridor which is trying to be established on our southern border and to bring peace and peace to the region,” Erdogan tweeted.The U.S.-backed Syrian Democratic Forces, or SDF, is militarily led by the Kurdish People’s Protection Units, or YPG, a group Ankara views as terrorists and a security threat on its southern border. The Turks stress the YPG’s ties to a separatist Kurdish group in Turkey, the PKK, which has carried out a decades-long violent insurgency against the Turkish state.”With the Operation Spring of Peace, we will eliminate the threat of terrorism towards our country. Thanks to the SAFE ZONE we will establish, we will ensure that Syrian refugees return to their countries. We will protect the territorial integrity of Syria, and free the people of the region from the clutches of terror,” Erdogan tweeted.Turkey’s long-expected incursion in northern Syria came less than a week after Trump spoke with Erdogan on the phone. After the call, the White House announced that “Turkey will soon be moving forward with its long-planned operation into Northern Syria” and “United States forces, having defeated the ISIS territorial ‘Caliphate,’ will no longer be in the immediate area.”Mustafa Bali, a spokesman for the SDF, tweeted Wednesday that “Turkish warplanes have started to carry out airstrikes on civilian areas.”Reuters reported later Wednesday that the SDF have halted their anti-ISIS operations as they deal with the Turkish offensive.Trump’s abrupt foreign policy move was met with immediate bipartisan criticism. Lawmakers from both major political parties accused the Trump administration of abandoning the Kurdish forces in the area who helped the U.S. fight ISIS.Among the most scathing comments came from Sen. Lindsey Graham, R-S.C., one of Trump’s closest allies in Congress who has nevertheless been one of his loudest critics on the withdrawal from Syria.A photo taken from Turkey’s Sanliurfa province, on October 09, 2019 shows smoke rises at the site of Ras al-Ayn city of Syria as Turkish troops along with the Syrian National Army begin Operation Peace Spring in northern Syria against PKK/YPG, Daesh terrorists.Kerem Kocalar | Anadolu Agency | Getty Images”Pray for our Kurdish allies who have been shamelessly abandoned by the Trump Administration. This move ensures the reemergence of ISIS,” the senator tweeted.Graham also vowed that he will “lead [the] effort in Congress to make Erdogan pay a heavy price.”Later Wednesday, NATO’s secretary-general Jen Stoltenberg urged Turkey not to “further destabilize the region,” though he said that the country has “legitimate security concerns” related to the threats of terrorism and an influx of refugees.Turkey and Kurdish groups have clashed for years, and Ankara recently signaled that it planned to carry out operations against the Kurds near Syria’s northern border with Turkey.Trump took to Twitter to justify the decision to withdraw.”It is time for us to get out of these ridiculous Endless Wars, many of them tribal, and bring our soldiers home,” Trump tweeted Monday. “WE WILL FIGHT WHERE IT IS TO OUR BENEFIT, AND ONLY FIGHT TO WIN.””Turkey, Europe, Syria, Iran, Iraq, Russia and the Kurds will now have to figure the situation out, and what they want to do with the captured ISIS fighters in their ‘neighborhood,'” the president wrote.On Wednesday, Trump followed up by railing against what he characterized as past botched attempts by the U.S. to meddle in the Middle East.”Now we are slowly & carefully bringing our great soldiers & military home,” Trump said. “Our focus is on the BIG PICTURE! THE USA IS GREATER THAN EVER BEFORE!”— CNBC’s Natasha Turak and John Schoen contributed to this report.