The Kurdish-led Syrian Democratic Forces said Turkish warplanes struck its region in the northeast, sparking 'huge panic among people'. Mustafa Bali, Syrian Democratic Forces spokesman, wrote on Twitter: 'Turkish warplanes have started to carry out air strikes on civilian areas.'
Syrian state media and a Kurdish official separately confirmed that bombing hit the town of Ras al-Ain in the northeast along the Turkish border. Earlier, Turkish television reports said Turkish jets had bombed Syrian Kurdish positions across the border from Turkey.
Mr Erdogan tweeted that the armed forces along with the Syrian National Army had launched 'Operation Peace Spring' to 'prevent the creation of a terror corridor' along the Turkish border.
He said that the aim is to eliminate threats from the Syrian Kurdish militia and the Islamic State militants and to enable the return of Syrian refugees in Turkey after the formation of a 'safe zone' in the area.
The Turkish president wrote on Twitter: 'Our mission is to prevent the creation of a terror corridor across our southern border, and to bring peace to the area. We will preserve Syria's territorial integrity and liberate local communities from terrorists.'
Syria vowed to respond to the Turkish invasion of the northeast of the country. The Syrian foreign ministry said the 'hostile actions' of the Turkish government revealed its 'expansionist ambitions,' saying an attack on Syrian territory 'could not be justified' and pledged to 'confront a Turkish assault'.
The Turkish leader declared an offensive against US-allied Kurdish fighters who effectively control northeastern Syria after a telephone conversation with Trump, who promised to withdraw US troops serving as a buffer.
Earlier Trump announced his decision to abandon America's Syrian Kurdish allies. President Trump tweeted that the US should have never used troops in the Middle East and referenced the failed bid to find Saddam Hussein's alleged weapons of mass destruction as the premise for the Iraq war under President George W. Bush as a reason for the US withdrawal from northern Syria.
Trump said he is 'slowly and carefully' bringing soldiers home from the Middle East, ending US involvement in what he described as the 'worst mistake' in the nation's history and winding down nearly two decades of American warfare.
Senator Lindsey Graham vowed today that Congress will inflict a cost on Turkey for its offensive against Syria's Kurds as the usually loyal ally of President Donald Trump sharply criticised US policy.
Mr Graham said that 'a disaster is in the making,' if Turkey entered Syria.
The senior Republican later tweeted, referring to Turkish President Recep Tayyip Erdogan: 'Pray for our Kurdish allies who have been shamelessly abandoned by the Trump Administration. This move ensures the reemergence of ISIS. Will lead effort in Congress to make Erdogan pay a heavy price.'
Damascus today said it 'is determined and willing to confront a Turkish assault using all legitimate means,' said a foreign ministry statement carried by state news agency SANA, condemning Ankara's 'hawkish statements, hostile intentions...and military build-up' along the border.
It said it held 'some Kurdish groups [in Syria] responsible' for the current situation on the border, but would still be ready to 'embrace' them if they decide to return to the fold.
Senators like Mitt Romney, Homeland Security Chair Ron Johnson, Energy Committee Chair Lisa Murkowski also accused Trump of 'betraying' and 'abandoning' the Kurds in Syria to no avail.
Anti-war Republican Senator Rand Paul was one of a handful of Republican lawmakers to openly hail Trump's decision.
'President Trump should be applauded for putting America first! I support bringing our troops home from endless wars in the Middle East!' he said on Tuesday evening.
The Turkish military offensive in Syria can be construed as a violation of Syria's sovereignty, Vladimir Dzhabarov, first deputy chair of the Foreign Affairs Committee in the upper house of parliament, has said.
Yet, Russia said it would not get involved in the conflict. Vladimir Putin told his Turkish counterpart Tayyip Erdogan by phone today to avoid any steps in Syria that could damage its peace process, the Kremlin said.
In the early part of the eight-year-old civil war in Syria, Kurdish forces took control of Kurdish-majority areas of the north and east and set up their own autonomous institutions.
When the Islamic State group swept across the region in 2014, they mounted a fierce defence of their heartland and became the US-led coalition's main military partner on the ground.
Ankara strongly opposed Washington's support for Kurdish forces in Syria citing their links to the outlawed Kurdistan Workers' Party (PKK) which has fought a deadly insurgency against the Turkish state since 1984.
Damascus rejects Kurdish self-rule and wants central government institutions restored in Kurdish-held areas. Weakened by Washington's decision to withdraw most of its troops following the capture of the last vestige of IS's 'caliphate' in March, the Kurdish-led alliance has opened talks with Damascus.
Ankara says the creation of a safe zone will allow for the return of Syrian refugees in Turkey, and create greater regional stability.
However, observers warn fresh conflict along the border will destabilise the region and likely lead to an ISIS resurgence as the Syrian Democratic Forces diverts forces to fight the Turks.
Overnight the Syrian Democratic Forces reported three suicide bomb attacks in Raqqa, the de facto capital of ISIS's self-declared Caliphate, by sleeper cells which had activated in the city.
Turkey wants to create what it calls a 'safe zone' in a stretch of territory along its southern border with Syria that is currently controlled by Syrian Kurdish fighters, known as the People's Protection Units, or YPG.
Turkey considers the YPG as terrorists affiliated with the outlawed Kurdistan Workers' Party, or PKK, which has waged a 35-year-long battle against the Turkish state. Ankara also views the YPG-controlled zone as an 'existential threat'.
Erdogan has demanded a 'safe zone' that is 20 miles deep and stretches more than 300 miles toward the Iraqi border.
He initially had hoped to do it in collaboration with the United States but grew frustrated with what he considered to be delaying tactics by the U.S.
Once secured, Turkey wants to resettle the area with 2 million Syrian refugees who fled to Turkey due to the conflict in their home country.
How such a massive resettlement would be carried out is unclear. Human rights groups have warned that any escalation of fighting in the area could displace hundreds of thousands more people.
Erdogan has spoken of plans to build towns, villages, hospitals and schools but also says Turkey, which has already spent some $40 billion on the refugees, cannot afford to do it alone.
He has said he will convene a donors conference to help meet the cost and has called on European nations to share the burden, warning that Turkey could be forced to open the 'gates' for an influx of migrants to Western nations.
Analysts say this operation would likely be more complicated.
Unwilling to let go of an area they wrested from the Islamic State group, the battle-hardened Kurdish fighters - trained and equipped by the U.S. - have vowed to fight the Turks until the end.