Akcakale, Turkey — Turkey launched airstrikes and fired artillery aimed at crushing Kurdish fighters in northern Syria on Wednesday after U.S. troops pulled back from the area, paving the way for an assault on forces that have long been allied with the United States. Turkish President Recep Tayyip Erdogan announced the start of the campaign, which followed an abrupt decision Sunday by U.S. President Trump that American troops would step aside to allow for the operation.

Mr. Trump's move has drawn harsh bipartisan opposition at home. It represents a shift in U.S. policy that essentially abandoned the Syrian Kurdish fighters who have been America's only allies inside Syria in the fight against ISIS.

Mr. Trump offered no explicit condemnation of Turkey in a statement Wednesday.

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"This morning, Turkey, a NATO member, invaded Syria," Mr. Trump said. "The United States does not endorse this attack and has made it clear to Turkey that this operation is a bad idea. There are no American soldiers in the area. From the first day I entered the political arena, I made it clear that I did not want to fight these endless, senseless wars — especially those that don't benefit the United States. 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 ..."

Smoke billows following Turkish bombardment on Syria's northeastern town of Ras al-Ain in the Hasakeh province along the Turkish border on October 9, 2019. Getty

After Turkey's offensive began, there was sign of panic in the streets of Ras al-Ayn- one of the towns under attack with residential areas close to the borders. Cars raced to safety, although it was not clear if they were leaving the town or heading away from border areas. Near the town of Qamishli, plumes of smoke were seen rising from an area close to the border after activists reported sounds of explosion nearby.

At least one member of the Kurdish-led force known as the Syrian Democratic Forces was killed in the Turkish bombardment, Kurdish activists and a Syria war monitor said.

Turkey's campaign — in which a NATO member is raining down bombs on an area where hundreds of U.S. troops are stationed — drew immediate criticism and calls for restraint from Europe.

"Coalition forces are not near the places Turkey has struck so far," an official with the U.S.-led coalition told The Associated Press.

CBS News national security correspondent David Martin reports that as part of the now abandoned joint patrols along the Turkish border, the U.S. had set up a Joint Operations Center in Turkey. That center is still being used to advise the Turks on the location of American troops.

The Kurdish forces have warned of a "humanitarian catastrophe" that could potentially unfold because of the Turkish military operation.

"Our mission is to prevent the creation of a terror corridor across our southern border, and to bring peace to the area," Erdogan said in a tweet.

He added that Turkish Armed Forces, together with Turkish-backed Syrian fighters known as the Syrian National Army, had begun what they called "Operation Peace Spring" against Kurdish fighters to eradicate what Erdogan said was "the threat of terror" against Turkey.

Minutes before Erdogan's announcement, Turkish jets began pounding suspected positions of Syrian Kurdish forces in the town of Ras al Ayn, according to Turkish media and Syrian activists. The sound of explosions could be heard in Turkey.

A photograph released to Turkish media showed Erdogan at his desk, reportedly giving orders for the start of the operation.

It was difficult to know what was hit in the first hours of the operation.

Mustafa Bali, a spokesman for the U.S.-backed Syrian Democratic Forces, said Turkish warplanes were targeting "civilian areas" in northern Syria, causing "a huge panic" in the region.

Turkish warplanes have started to carry out airstrikes on civilian areas. There is a huge panic among people of the region. — Mustafa Bali (@mustefabali) October 9, 2019

Before Turkey's attack, Syrian Kurdish forces that are allied with the U.S. issued a general mobilization call, warning of a "humanitarian catastrophe."

The Turkish operation meant to create a so-called "safe zone" carries potential gains and risk for Turkey by getting even more deeply involved in the Syria war. It also would ignite new fighting in Syria's 8-year-old war, potentially displacing hundreds of thousands.

Turkey has long threatened to attack the Kurdish fighters whom Ankara considers terrorists allied with a Kurdish insurgency in Turkey. AP journalists on the Turkish side of the border overlooking Tal Abyad saw Turkish forces crossing into Syria in military vehicles.

Expectations of an invasion increased after Trump's announcement, although he also threatened to "totally destroy and obliterate" Turkey's economy if the Turkish push into Syria went too far.

In the U.S., Republican critics and others said he was sacrificing an ally, the Syrian Kurdish forces, and undermining Washington's credibility. Mr. Trump tweeted that he is focused on the "BIG PICTURE" that does not include American involvement in "stupid endless wars" in the Middle East.

....IN THE HISTORY OF OUR COUNTRY! We went to war under a false & now disproven premise, WEAPONS OF MASS DESTRUCTION. There were NONE! Now we are slowly & carefully bringing our great soldiers & military home. Our focus is on the BIG PICTURE! THE USA IS GREATER THAN EVER BEFORE! — Donald J. Trump (@realDonaldTrump) October 9, 2019

Turkey "has legitimate security concerns" after suffering "horrendous terrorist attacks" and hosting thousands of refugees, said NATO Secretary-General Jens Stoltenberg.

But he also said in Rome that Turkey should not "further destabilize the region" with its military action in Syria.

German Foreign Minister Heiko Maas condemned the offensive, saying it will "further destabilize the region and strengthen IS." The operation also was criticized by European Commission President Jean-Claude Juncker.

The EU is paying Turkey 6 billion euros ($6.6 billion) to help the country cope with almost 4 million Syrian refugees on its territory in exchange for stopping migrants leaving for Europe. But Ankara seeks more money amid concerns that thousands of Syrians could soon cross its border.

Fahrettin Altun, the Turkish presidency's communications director, called on the international community to rally behind Ankara, which he said would also take over the fight against ISIS.

Turkey aimed to "neutralize" Syrian Kurdish militants in northeastern Syria and to "liberate the local population from the yoke of the armed thugs," Altun wrote in a Washington Post column published Wednesday.

Erdogan discussed plans for the incursion by phone with Russian President Vladimir Putin. Erdogan's office said he told Putin the military action in the region east of the Euphrates River "will contribute to the peace and stability" and also "pave the way for a political process" in Syria.

In its call for a general mobilization, the local civilian Kurdish authority known as the Autonomous Administration of North and East Syria asked the global community to live up to its responsibilities as "a humanitarian catastrophe might befall our people."

The Kurds also said they want the U.S.-led coalition to set up a no-fly zone in northeastern Syria to protect the civilian population from Turkish airstrikes.

The U.S.-backed Syrian Kurdish group urged Moscow to broker and guarantee talks with the Syrian government in Damascus in light of the military operation. The Syrian Kurdish-led administration said it is responding positively to calls from Moscow encouraging the Kurds and the Syrian government to settle their difference through talks.

Syria's Foreign Ministry condemned Turkey's plans, calling it a "blatant violation" of international law and vowing to repel an incursion. He said some Kurdish groups were being used as a tool to help an alleged "American project," but added Syria is ready to welcome back its "stray sons if they return to their senses," referring to the pro-U.S. Kurdish fighters.

Russian Foreign Minister Sergey Lavrov accused Washington of playing "very dangerous games" with the Syrian Kurds, saying that the U.S. first propped up the Syrian Kurdish "quasi state" in Syria and now is withdrawing its support.

"Such reckless attitude to this highly sensitive subject can set fire to the entire region, and we have to avoid it at any cost," he said in Kazakhstan. Russian news media said Moscow communicated that position to Washington.

Earlier Wednesday, ISIS militants targeted a post of the Kurdish-led Syrian Democratic Forces in the northern Syrian city of Raqqa, which was once the de facto ISIS capital at the height of the militants' power in the region.