Turkey launched airstrikes, fired artillery and began a ground offensive against 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.

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

Turkish President Recep Tayyip Erdogan on Wednesday announced the start of the campaign, which followed an abrupt decision Sunday by U.S. President Donald Trump that American troops would step aside to allow for the operation. The decision marked a sudden shift in U.S. policy that essentially abandoned the Syrian Kurds, longtime U.S. allies in the fight against ISIS in Syria.

Trump's move drew bipartisan opposition at home and represented a shift in U.S. policy that essentially abandoned the Syrian Kurdish fighters who have been America's only allies in Syria fighting the Islamic State group. After Erdogan announced the offensive, Trump called the operation "a bad idea."

Trump had cast his decision to pull back U.S. troops from parts of northeast Syria as fulfilling a campaign promise to withdraw from the "endless war" in the Middle East. Republican critics and others said he was sacrificing an ally, the Syrian Kurdish forces, and undermining Washington's credibility.

Sen. Lindsey Graham, R-S.C., a steadfast Trump supporter, was uncharacteristically critical of the administration in a series of tweets Wednesday, saying that Turkey entering northern Syria is "a disaster in the making."

"Pray for our Kurdish allies who have been shamelessly abandoned by the Trump Administration. This move ensures the reemergence of ISIS," he tweeted. "I urge President Trump to change course while there is still time by going back to the safe zone concept that was working."

Sen. Mitt Romney of Utah tweeted that the attack on Kurdish allies was "a tragic loss of life among friends shamefully betrayed," and expressed hope that Trump's decision "does not lead to even greater loss of life and a resurgence of ISIS."

The president lashed out over the sharp bipartisan criticism, saying he is focused on the "BIG PICTURE" that does not include American involvement in "stupid endless wars" in the Middle East.

"Fighting between various groups that has been going on for hundreds of years. USA should never have been in Middle East," Trump said in a series of morning tweets. "The stupid endless wars, for us, are ending!"

Republican Sen. Rand Paul of Kentucky came to Trump's defense, echoing the president in asserting the value of pulling U.S. troops from overseas to stop "endless wars." Paul said Trump is the first president in his lifetime "to understand what is our national interest," and he criticized other politicians' support for costly yearslong U.S. military engagements abroad.

The United Nations Security Council will hold a meeting Thursday on Turkey's milirary action in Syria, South African Ambassador to the United Nations Jerry Matthews Matjila confirmed to reporters. Five European nations on the council — France, United Kingdom, Germany, Belgium and Poland — requested the meeting, according to two diplomatic officials.

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. By nighttime, there were fires in one of the town's neighborhoods, apparently ignited by the shelling.

"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 Kurdish-led Syrian Democratic Forces, said Turkish warplanes were targeting "civilian areas" in northern Syria, causing "a huge panic" in the region.

Before Turkey's attack, Syrian Kurdish forces that are allied with the United States 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. Associated Press journalists on the Turkish side of the border overlooking Tal Abyad saw Turkish forces crossing into Syria in military vehicles Wednesday.

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 another statement Wednesday Trump clarified that he did not support Turkey's strikes on the Kurdish fighters.

"The United States does not endorse this attack and has made it clear to Turkey that this operation is a bad idea," Trump said.

He said no American soldiers are in the area and that the U.S. will monitor the situation closely.

Turkey had been massing troops for days along its border with Syria and vowed it would go ahead with the military operation and not bow to the U.S. threat.

Fahrettin Altun, the Turkish presidency's communications director, called on the international community in a Washington Post op-ed published Wednesday 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.

Erdogan discussed plans for the incursion with Russian President Vladimir Putin. Erdogan's office said the Turkish leader told his Russian counterpart by phone that the planned 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, also asked the international community to live up to its responsibilities as "a humanitarian catastrophe might befall our people."

The Kurds also said that 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 Turkey's planned military operation. The Syrian Kurdish-led administration said in a statement 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. Although it blamed some Kurdish groups for what is happening, saying they were being used as a tool to help an alleged "American project," it said 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 northeastern Syria and is now 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 during a visit to Kazakhstan. Russian news media said Moscow communicated that position to Washington.

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

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.

The SDF, which is holding thousands of ISIS fighters in several detention facilities in northeastern Syria, has warned that a Turkish incursion might lead to the resurgence of the extremists. The U.S.-allied Kurdish-led force captured the last ISIS area controlled by the militants in eastern Syria in March.

In the ISIS attack, three suicide bombers struck Kurdish positions in Raqqa. There was no immediate word on casualties. An activist collective known as Raqqa is being Silently Slaughtered reported an exchange of fire and an explosion.

The Observatory said the attack involved two ISIS fighters who engaged in a shootout before blowing themselves up.

ISIS claimed responsibility, saying one of its members killed or wounded 13 SDF members.

Also Wednesday, Iranian state TV reported a surprise military drill with special operations forces near the country's border with Turkey, in Iran's Western Azerbaijan province. The TV didn't mention the expected Turkish offensive into Syria or elaborate on the reasons for the drill.

Mroue reported from Beirut. Associated Press writers Suzan Fraser in Ankara, Turkey; Mehmet Guzel in Akcakale, Turkey; Nasser Karimi in Tehran, Iran; and Nataliya Vasilyeva in Moscow contributed.