Turkey announced Wednesday that its ground forces invaded northeastern Syria to fight against Kurdish forces just hours after launching an initial assault in the area, as the first reports of deaths emerged.

Turkish President Recep Tayyip Erdogan launched Operation Peace Spring on Wednesday after President Trump announced the U.S. would withdraw American troops from the area, a move considered by many analysts a blow to the U.S.-backed Kurdish forces there. Erdogan said the mission was to "neutralize terror threats against Turkey and lead to the establishment of a safe zone, facilitating the return of Syrian refugees to their homes."

At least seven civilians were killed in Turkish strikes in northeastern Syria since the country launched an assault Wednesday morning, according to activists and a war monitor.

Trump told reporters Wednesday that he would do "far more than sanctions" against Turkey if the country didn't act in the most "humane way as possible," and that he hoped Erdogan would act rationally. When asked what would happen if Erdogan wiped out the Kurds, Trump threatened to "wipe out" Turkey's economy, saying he'd done it once before.

TRUMP CALLS TURKEY ASSAULT ON SYRIA A 'BAD IDEA' AS KURDS REPORT CIVILIAN DEATHS

Kurdish forces in northeastern Syria were guarding thousands of captured Islamic State (ISIS) fighters with the help of the U.S. in the area.

The president said the captured terrorists were "really bad people who should go back to Europe."

Earlier Wednesday, Trump warned Turkey that its initial assault was a "bad idea."

"The United States does not endorse this attack and has made it clear to Turkey that this operation is a bad idea," Trump said in a White House statement. "Turkey has committed to protecting civilians, protecting religious minorities, including Christians, and ensuring no humanitarian crisis takes place -- and we will hold them to this commitment."

A spokesperson for the Kurdish-led Syrian Democratic Forces said Wednesday that Turkish forces "started to carry out airstrikes on civilian areas" and caused a "huge panic among people of the region."

U.S. military officials told Fox News the president ordered the U.S. military not to get involved in the strikes, after the Kurds requested air support from American forces.

A group of Turkish forces first entered northeastern Syria on Wednesday morning near Tal Abyad and Ras al-Ayn, Bloomberg had reported. Artillery units later shelled suspected Syrian Kurdish targets in Tal Abayd, while two mortar shells hit the Turkish border town of Ceylanpinar, according to Turkey's state-run Anadolu news agency.

"We said to various countries, we'd like you to take your people back. Nobody wants them, they're bad," Trump said, adding that "maybe the Kurds [...] if not them, Turkey" would deal with the ISIS fighters.

If the fighters escape, they would "go back to Europe," according to the president.

Trump said the situation was "not a fair deal" for the U.S., and that going into the Middle East was the "worst mistake the U.S. has ever made."

"We're doing jobs that [Europe, Russia, Iran, Iraq, Turkey, Syria] should be doing. [...] We're 7,000 miles away," he said.

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President Trump announced Sunday the U.S. would pull American troops out of northern Syria, a move leaving the U.S.-backed Kurdish forces -- longtime allies in the fight against ISIS in Syria -- in peril. Ankara has considered the Syrian Kurdish forces to be terrorists allied with a Kurdish insurgency within Turkey.

Fox News’ Jennifer Griffin, Lucas Tomlinson, Greg Norman, Victor Garcia, Dom Calicchio and The Associated Press contributed to this report.