Turkish President Tayyip Erdogan attends a news conference at Huber Mansion in Istanbul, Turkey March 31, 2019.Murad Sezer | ReutersTurkey’s President Recep Tayyip Erdogan threatened Europe with a flood of refugees if the continent’s leaders call the Turkish invasion of Syria an “occupation” during a speech to local lawmakers Thursday.”We will open the gates and send 3.6 million refugees your way,” Erdogan said, according to Reuters, while speaking to officials from his ruling AK Party.A Turkish offensive in northern Syria has been underway since Wednesday, with airstrikes and artillery fire targeting U.S.-allied Kurdish forces on the ground.The operation began just days after President Donald Trump made a surprise announcement withdrawing U.S. troops from a part of Syria that had been reclaimed in a bloody and drawn-out war between the U.S.-led coalition and the so-called Islamic State. Trump framed his decision as one that would hand the responsibility of containing IS to the Turks.Ground fighting since 2014 against the extremist group was spearheaded by Kurdish forces that made up the bulk of the Syrian Democratic Forces, a U.S.-backed organization now tasked with governance of the area and containment of resurgent IS fighters and overcrowded IS prisons. In particular instances, when asked for help in the anti-IS fight, Turkey refused to help the Kurdish forces, which it reportedly sees as a greater threat than IS.Erdogan has pledged to clear the area of “terrorists,” and says his aim is to allow a path for the return of Syrian refugees in Turkey to go back home. Numerous U.S. officials have cast doubt on that promise.Ankara has long vowed to wipe out the Kurdish militia presence along its border in northern Syria, which it views as a security threat and indistinguishable from a separate Kurdish terrorist group that is waging a counterinsurgency inside Turkey.The Turkish military confirmed Wednesday it had “launched the land operation into the east of the Euphrates river” and said it had hit more than 100 “militant targets.””The operation is currently continuing with the involvement of all our units… 109 terrorists have been killed so far,” Erdogan said, without specifying whether this meant IS fighters or the Kurdish militia members Ankara also calls terrorists.Activists on the ground say at least seven civilians have been killed so far. Video footage showed civilians trying to flee as dark plumes of smoke rose on the horizon.European Commission President Jean-Claude Juncker on Wednesday expressed concern over the offensive and called on Turkey to show restraint.”Turkey has security concerns at its border with Syria, that we must understand. However, I call on Turkey, as well as other actors, to act with restraint,” Juncker told the EU Parliament.A spokesperson for U.K. Prime Minister Boris Johnson expressed the British government’s “grave concern,” saying “we do not support the action” by Turkey. EU diplomats have warned of a fresh humanitarian crisis and a setback in the ongoing effort to counter and contain IS.Turkey hosts the largest number of refugees in the world, with 3.6 million registered Syrian nationals in 2018 and 40,000 refugees and asylum-seekers of other nationalities, according to the UN High Commissioner for Refugees.