President Recep Tayyip Erdogan on Tuesday warned the United States to withdraw any American forces from the Syrian town of Manbij, vowing Turkish troops would expand a cross-border military operation to the key strategic hub.

Erdogan blamed Washington for the presence in Manbij of fighters from the Peoples' Protection Units (YPG) and its Democratic Union Party (PYD) political wing, which Ankara sees as terror groups.

Turkey on January 20 launched a major operation aimed at ousting YPG forces from their enclave of the northwestern town of Afrin. However moving east to Manbij -- where unlike Afrin there is a US military presence -- would mark a major escalation.

Accusing Washington of breaking past promises, Erdogan said: ‘They (Americans) told us they will pull out of Manbij. They said they will not stay in Manbij... Why don't you just go?’

‘Who did you bring there? PYD. Who did you bring there? YPG. Who did you bring there? PKK,’ he said.

‘And then you tell us not to come to Manbij! We will come to Manbij to return it to its original owners,’ he added.

Turkey considers towns like Manbij to be originally Arab-majority territory whose ethnic balance was upset in favour of the Kurds during the seven-year civil war.

Turkey's Western allies, including the United States, do not classify the YPG as a terror group and have worked closely with its fighters in the battle against Islamic State militants.

In 2016, the Syrian Democratic Forces (SDF), an alliance dominated by the YPG, captured Manbij from IS.

In a show of anger at Turkey's NATO ally, Erdogan asked the United States what it was doing in Syria in the first place.

‘You do not have a border, you are not a neighbour (of Syria),’ he said. ‘What's your business there? We have a 911 kilometre (566 miles) border.’

Erdogan also accused US President Donald Trump and his predecessor Barack Obama of failing to tell the truth over US support for the YPG.

‘They told us many things but unfortunately they did not tell the truth,’ Erdogan said. ‘Mr Obama did not tell the truth and now Mr Trump is heading down the same path.’