(CNN) Turkey began a planned military offensive into northeastern Syria on Wednesday, launching airstrikes and artillery fire across the border just days after the Trump administration announced it was pulling US troops back from the area.

The operation is aimed at pushing Kurdish forces -- who were a key ally of the US in the fight against ISIS -- away from Turkey's border.

"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," Turkey's President Recep Tayyip Erdogan tweeted as he announced the start of the operation.

The Syrian Democratic Forces (SDF) who operate in the area are US allies. They are led by the Kurdish People's Protection Units (YPG), which Turkey considers a terrorist organization.

As a barrage of airstrikes and artillery fire volleyed into northern Syria , chaotic scenes unfolded on the ground as people tried to flee to safety. Roads were gridlocked with hundreds of fleeing families, motorcycles piled with five to six people and mattresses strapped to cars.

Reports began to filter in on Wednesday following the aerial bombardment, with the SDF tweeting that two civilians had been killed and two others injured in the village of Misharrafa, west of Ras al-Ain.

The SDF said civilian homes in the village of Sikarkah in eastern Qamishli and areas near the Bouzra dam in Derik -- which provides water to hundreds of thousands of civilians in northern Syria -- were also targeted.

The SDF suspended their counter-ISIS operations amid the bombardment in order to focus on the Turkish offensive.

"We will clash against the Turks to not allow them to cross the border. We will use all our possibilities against Turkish aggression," the group's spokesman Mustafa Bali tweeted.

Wednesday night, Turkey's Defense Ministry wrote on their verified Twitter account: "The Turkish Armed Forces and the Syrian National Army have launched the land operation into the east of the Euphrates river as part of the Operation Peace Spring."

The Syrian National Army is considered the biggest umbrella group for the factions of the Turkish-backed Free Syrian Army.

Bali tweeted later that the SDF had turned back the ground incursion near the border town of Til Abyad. "No advance as of now," he wrote.

The offensive comes days after US President Donald Trump provoked a storm of criticism, including from his own party, by announcing the pullback of US military forces from northeast Syria.

#Qamishli city in NE #Syriya during the Turkish air striks. pic.twitter.com/cCfQefFE7v — Coordination & Military Ops Center - SDF (@cmoc_sdf) October 9, 2019

Trump: Turkey operation is a 'bad idea'

Trump defended Wednesday his decision to withdraw troops from northern Syria, but added that the US "does not endorse" Turkey's operation.

"The United States does not endorse this attack and has made it clear to Turkey that this operation is a bad idea," the President said in a statement from the White House.

"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 ... We expect Turkey to abide by all of its commitments, and we continue to monitor the situation closely."

A photo taken from Turkey's Sanliurfa province shows smoke rising at the site of Ras al-Ain.

Turkey's Minister of National Defense, Hulusi Akar, tweeted that the United States, United Nations and NATO, among others, had been informed of the operation at 7 a.m. ET.

Ahead of the offensive Wednesday, Syria condemned Turkey's "aggressive behavior" and "hostile intentions," according to Syrian state news agency SANA. "The aggressive behavior of the Erdogan regime clearly shows the Turkish expansionist ambitions in the territory of the Syrian Arab Republic and cannot be justified under any pretext," a source at the Foreign Ministry said, SANA reported.

A source at the Foreign Ministry said in a statement Wednesday that the Syrian government holds some Kurds responsible for what is happening "as a result of their dependence on the American project."

Meanwhile, Russian President Vladimir Putin asked Erdogan to "carefully weigh the situation" in Syria, so as not to "harm the overall efforts to resolve" the crisis, according to a statement released by the Kremlin.

In the statement, the Kremlin also underlined "the importance of ensuring the unity and territorial integrity of Syria and respect for its sovereignty was noted on both sides."

Widespread condemnation

Bahrain and Egypt's Foreign Ministries issued statements condemning the Turkish operation in Syria and called for an emergency meeting of the Arab League.

Saudi Arabia condemned the offensive, according to an official source cited by state TV, warning that the incursion could have negative repercussions on the security of the region.

Kuwait and the United Arab Emirates also issued statements about the fighting.

A statement from the UAE Ministry of Foreign Affairs and International Cooperation said that the "aggression" represents a serious development and an "unacceptable, flagrant assault on the sovereignty of a brotherly Arab state in defiance of international law and blatant interference in Arab affairs," according to the state-run Emirates News Agency.

UK Foreign Secretary Dominic Raab expressed his "serious concern" over Wednesday's events.

"This risks destabilizing the region, exacerbating humanitarian suffering, and undermining the progress made against (ISIS) which should be our collective focus," Raab said in a statement issued by the UK Foreign and Commonwealth Office.

Calls to avoid a 'possible humanitarian catastrophe'

The SDF called on the international community Tuesday to help avoid a possible humanitarian disaster.

In a series of tweets from the verified Twitter account of the SDF, the General Command said the border areas of northeast Syria "are on the edge of a possible humanitarian catastrophe." It went on to call on the international community and those countries fighting against ISIS "to carry out their responsibilities" to avoid a "possible impending humanitarian disaster."

The SDF, which has vowed to defend itself against any perceived Turkish incursion, called on the US-led coalition and the international community to implement a no-fly zone over northern Syria similar to the one implemented in Iraq.

The Turkish Defense Ministry said Tuesday that the Turkish military was "the only coalition and NATO army fighting the DAESH (ISIS) terrorist group in the Euphrates Shield Operation."

"Turkey is one of the countries most affected by DAESH's bloody activities and has fought against this terrorist organization both domestically and beyond its borders with increasing tempo and intensity," the ministry said in a tweet posted on its official twitter page.

The Euphrates Shield operation, launched in August 2016 inside Syrian territory, was not only aimed at fighting ISIS but also the YPG.

On Wednesday, the SDF said ISIS "sleeper cells" attacked Kurdish positions in Raqqa, Syria, in the early hours, as tweeted by Bali, head of the SDF press office.

Manbij Military Council spokesman, Shervan Derwish, also tweeted about the attack citing security sources saying, "more than 50 armed Daesh group in Raqqa are launching a coordinated attack to control Al Basel base in center of the city."

On Saturday, Erdogan announced that the country had "completed our preparations and action plan" and was ready to launch a "ground and air operation" east of the Euphrates river, with the goal of establishing "peace" by clearing the region of "terrorists."

Reinforcements deployed by the Turkish army could be seen arriving at the border town of Akcakale on Tuesday, according to the state-owned Anadolu news agency.

Turkey won't 'bow to threats'

Turkish army soldiers drive towards the border with Syria near Akcakale in Sanliurfa province on October 8, 2019.

The Kurds have long been considered as among Washington's most reliable partners in Syria and in the broader campaign against ISIS in the region.

US-backed Kurdish forces have been responsible for holding all captured ISIS fighters in the area. However, according to the White House, this responsibility will now fall to Turkey.

But a senior adviser to President Erdogan told CNN on Wednesday that Turkey "never said" that it would "shoulder the burden" of the imprisoned ISIS fighters alone.

"We will safeguard any areas that contain these prisons. However, we would like the management of the camps, in particular, something that has to be undertaken as a joint effort with the international community," Gülnur Aybet said.

On Monday, Trump said he was "not siding with anybody" -- Kurdish forces or the Turkish government -- and reiterated an earlier warning to Turkey about potential economic devastation.

"I told Turkey if they do anything outside of what we think is humane ... they could suffer the wrath of an extremely decimated economy," the Trump said.

Turkish Vice President Fuat Oktay said his country wouldn't "bow to threats" in an apparent response to Trump's warning.

Correction: This story has been updated to correct the date Turkey launched Operation Euphrates Shield. A previous version of a map incorrectly located the Al-Hol camp. It has been updated.