Turkey said it began a military operation against Kurdish forces in northeastern Syria on Wednesday, days after the Trump administration announced the US was pulling troops from the region.

"The Turkish Armed Forces, together with the Syrian National Army, just launched #OperationPeaceSpring against PKK/YPG and Daesh terrorists in northern Syria. Our mission is to prevent the creation of a terror corridor across our southern border, and to bring peace to the area," Turkish President Recep Tayyip Erdogan said in a statement.

US President Donald Trump's decision to withdraw troops from northeastern Syria was widely viewed as greenlighting a Turkish military incursion and criticized heavily by congressional Republicans.

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Turkey began an expected military operation against US-backed Kurdish forces in northeastern Syria on Wednesday, Turkish President Recep Tayyip Erdogan announced.

Erdogan in a tweet said: "The Turkish Armed Forces, together with the Syrian National Army, just launched #OperationPeaceSpring against PKK/YPG and Daesh terrorists in northern Syria. Our mission is to prevent the creation of a terror corridor across our southern border, and to bring peace to the area."

The Turkish leader said the operation's goal 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."

"We will preserve Syria's territorial integrity and liberate local communities from terrorists," he added.

Turkey views the Syrian Kurdish People's Protection Units, or YPG, as a terrorist affiliate because of its association with the Kurdistan Workers' Party, or PKK, which since the mid-1980s has waged a violent campaign against the Turkish government as it seeks to establish an independent Kurdish state within Turkey.

Turkey launched the operation just a few days after Trump abandoned the Kurds

The Turkish operation against Kurdish forces began three days after the Trump administration abruptly announced it was withdrawing US troops stationed in the region. The move — which led to widespread criticism, including from congressional Republicans — came after a phone call between US President Donald Trump and Erdogan.

The decision was seen as the US abandoning the Kurds to a potential massacre by Turkey. The Kurds bore the brunt of the US-led campaign against the terrorist group ISIS and had previously been given assurances by the US that if they dismantled defensive positions along the border they would be protected from a Turkish assault.

Read more: Trump's decision to abandon the Kurds in Syria sends a dangerous message to US allies around the world

Ahead of the Turkish military incursion, the Kurdish-led Syrian Democratic Forces issued a desperate plea to the international community and countries that fought as part of the US-led coalition against ISIS to "carry out their responsibilities to avoid a possible impending humanitarian disaster."

"This attack will spill the blood of thousands of innocent civilians because our border areas are overcrowded," the SDF's official Twitter account said.

The SDF on Wednesday also called on the US and its allies to establish a no-fly zone to protect it from the Turkish assault.

There are also broad concerns that the Turkish operation will create a security vacuum, opening the door for the resurgence of ISIS in the region while benefiting Syrian President Bashar Assad as well as Russia and Iran, countries the Syrian government is allied with.

The Kurdish forces that Turkey is targeting are detaining thousands of ISIS fighters, and US lawmakers have expressed consternation that a Turkish incursion could pave the way for their escape.

Republican Sen. Lindsey Graham, who sits on the Senate Foreign Relations Committee and has been particularly critical of Trump's recent decision on Syria, on Wednesday morning tweeted: "Pray for our Kurdish allies who have been shamelessly abandoned by the Trump Administration. This move ensures the reemergence of ISIS."

Trump ahead of the military incursion: 'The stupid endless wars, for us, are ending!'

Ahead of Erdogan's announcement about the onset of the military incursion, Trump in a tweet characterized the impending clash between Turkish and Kurdish forces as "fighting between various groups that has been going on for hundreds of years."

"USA should never have been in Middle East. Moved our 50 soldiers out," Trump added. "Turkey MUST take over captured ISIS fighters that Europe refused to have returned. The stupid endless wars, for us, are ending!"

The Trump administration has said it does not endorse Turkey's assault on Kurdish forces, and it has rejected the notion that the withdrawal of US forces from northeastern Syria offered Erdogan a green light for a military incursion.

Amid the backlash from congressional lawmakers and former US officials, including former members of his administration, Trump earlier this week told Turkey he would "obliterate" its economy if in his "great and unmatched wisdom" he finds it has done something "off limits."

Trump said the Turkish invasion is a 'bad idea' but has no immediate plans to respond

When asked by Insider whether Trump planned to take any actions against Turkey over the military incursion, the White House provided a statement from the president that did not indicate any immediate response.

"This morning, Turkey, a NATO member, invaded Syria. The US does not endorse this attack and has made it clear to Turkey that this operation is a bad idea," Trump said in the statement.

The president went on to say that there are no US soldiers in the area, adding, "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 US."

Trump said 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."

The president said Turkey is also now responsible for "ensuring all ISIS fighters being held captive remain in prison and that ISIS does not reconstitute in any way, shape, or form" and that the US expects Turkey to continue to abide by its commitments. Trump said he'll continue to monitor the situation closely.