Turkish troops have entered north-eastern Syria, launching a land offensive against Kurdish militia fighters just days after US troops pulled back from the area.

Key points: The overnight military action follows Wednesday's strikes by Turkish warplanes and artillery aimed at Kurdish YPG targets

The overnight military action follows Wednesday's strikes by Turkish warplanes and artillery aimed at Kurdish YPG targets World leaders are concerned the offensive could destabilise the region and see an IS resurgence

World leaders are concerned the offensive could destabilise the region and see an IS resurgence Turkey's President Recep Tayyip Erdogan said operation "Peace Spring" was aimed at eradicating "the threat of terror"

The overnight military action follows Wednesday's strikes by Turkish warplanes and artillery aimed at Kurdish YPG targets, part of an operation announced by President Recep Tayyip Erdogan on his official Twitter account.

The Turkish defence ministry said the army had hit a total of 181 militant targets with air strikes and howitzers since the start of operation.

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Mr Erdogan said operation "Peace Spring" was aimed at eradicating "the threat of terror" against Turkey.

Turkey views Kurdish YPG fighters in north-east Syria as terrorists because of their ties to militants waging an insurgency inside Turkey, and an influx of non-Kurdish Syrians would help it secure a buffer against its main security threat.

Turkey has said it intends to create a "safe zone" in order to return millions of refugees to Syrian soil.

Kurdish-led forces in north-eastern Syria said the Turkish bombing killed five civilians and injured dozens more on Wednesday.

The Britain-based Syrian Observatory for Human Rights put the death toll at eight, including women and children.

The Kurdish-led Syrian Democratic Forces (SDF) said in a tweet that one of the airstrikes had already hit a prison holding detained IS militants.

'They're going to be escaping to Europe'

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 18 seconds 18 s US President not worried about ISIS fighters escaping Syria

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US President Donald Trump, during a press conference at the White House on Wednesday (local time), dismissed worries that captured IS fighters might escape in the chaos of a Turkish attack.

He said many of these fighters were of European origin and he had given European nations four chances to take responsibility for them.

Asked if he had any concerns that some of these IS fighters could escape and pose a threat elsewhere, Mr Trump adopted a dismissive tone.

"Well, they're going to be escaping to Europe. That's where they want to go," he said.

Mr Trump went on to criticise the Kurds for only fighting with the US over their own lands.

"They didn't help us in the Second War War, they didn't help us with Normandy."

Weapons 'black market is in full swing'

Mr Erdogan said operation "Peace Spring" was aimed at eradicating "the threat of terror" against Turkey. ( AP )

The SDF has said it has 40,000 fighters who will defend themselves against the Turkish onslaught, but they are heavily outgunned by Turkey.

While the US armed and trained the SDF, Washington held back from supplying its Kurdish allies with a more sophisticated arsenal, reflecting the needs of the battle but also Turkish concerns.

"The heaviest weapons we got from the US are some mortar shells, nothing heavier. No missiles, no anti-aircraft weapons, no anti-tank," said a member of the Kurdish forces, speaking on the condition of anonymity.

But another Kurdish fighter said the group had sourced anti-tank missiles on their own.

"Our duty is to resist. This is the Middle East and the black market is in full swing," the source said.

A US defence official, who also spoke on the condition of anonymity, and a Kurdish official in Syria said the SDF had suspended operations against IS militants because of the Turkish operation.

The Turkish military bombed the Syrian town of Tal Abyad. ( AFP: Bulent Kilic )

Turkey had been poised to advance into the area since US troops began withdrawing in an abrupt policy shift by Mr Trump, widely criticised in Washington as a betrayal of America's Kurdish militia allies.

Mr Trump announced the decision after a phone call with Mr Erdogan on Sunday evening (local time).

But on Wednesday Mr Trump said the US did not endorse Turkey's assault on northern Syria and had made it clear to Ankara that its incursion against Kurdish fighters who helped the US battle the Islamic State (IS) group was a "bad idea".

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Mr Trump added that no American soldiers were stationed in the area being invaded.

Republican senator Lindsay Graham, who is usually a vocal ally of Mr Trump, has repeatedly criticised the President's decision to withdraw US troops, and expressed concerns over the fate of Kurds in the area.

He told media outlet Axios that the sanctions would strike the Turkish economy and military, and predicted the Senate could marshal the votes to override any potential presidential veto.

"Who the hell supports Erdogan over the Kurds?" he said.

Mr Graham predicted "a devastating ripple effect" from Turkish action in Syria, warning that Mr Trump's decision to withdraw the troops opened the way for a Turkish strike on Kurdish-led forces long allied with Washington.

"The President's doing this completely against everybody else's advice. He will get 100 per cent of the credit if he knows something the rest of us don't. And he's going to get 100 per cent of the blame. There'll be no middle ground," Mr Graham said.

Australia fears IS resurgence

Prime Minister Scott Morrison said the Australian Government was "deeply concerned" about Turkey's actions in Syria, and about the "potential for the resurgence of Daesh", or the Islamic State.

He said Australia was using diplomatic channels to monitor the situation to help determine what "possible international responses" could be taken.

"We are concerned about what we're seeing of the actions of the Turkish Government moving into Syria, and what that could mean for the safety of people in that area," he said.

"We are also very concerned about what this could potentially mean for the Kurdish people.

"We have conveyed those concerns and will continue to convey those concerns directly and we will continue to work closely with the United States and others in terms of what, if any, potential response is to that quite serious situation on the ground."

Turkish offensive 'risks destabilising the region'

World powers fear the action could open a new chapter in Syria's war and worsen regional turmoil. ( AFP: Bulent Kilic )

World powers fear the action could open a new chapter in Syria's war and worsen regional turmoil.

Britain's Foreign Secretary Dominic Raab said on Wednesday he had "serious concerns" about Turkey's offensive.

"This risks destabilising the region, exacerbating humanitarian suffering, and undermining the progress made against Daesh which should be our collective focus," Mr Raab said in a statement.

European Commission president Jean-Claude Juncker called on Turkey to halt its military actions and warned the EU would not help pay to set up any safe zone in north-eastern Syria.

The Turkish offensive was also condemned by nations across the Middle East, Europe and beyond, including Saudi Arabia, Canada and Egypt.

Mr Erdogan earlier told Russia's President Vladimir Putin in a phone call that the operation would help peace and stability in Syria.

But Syria said it was determined to confront any Turkish aggression by all legitimate means.

Reuters/AP