Erdogan said a military operation would take place "any moment now", east of the Euphrates - an area where US-backed Syrian Democratic Forces are present.
Such a manoeuvre could put US troops into the firing line of the Turkish military, although Erdogan insisted that no NATO allies would be harmed in the operation.
"We can start our operation any moment now in Syrian territory at any place, especially along the 500 kilometre border, without harming US soldiers," Erdogan said, according to the Anadolu agency.
"We talked to [US President Donald] Trump. These terrorists have to leave areas east of the Euphrates. If they do not leave, we will dispatch them. Because they are disturbing us," he told a rally in Turkey.
Erdogan vowed last week to crush the Kurdish People's Protection Units (YPG) militia, which operates on the Turkish-Syria border, saying a new operation against the group would take place soon.
Turkish forces have been deployed towards the Syria border in great numbers, but sources have told The New Arab that an offensive is not actually expected as soon as has been hinted.
Ankara accuses the YPG of being affiliated with the Kurdistan Workers' Party (PKK), which has been proscribed as a terrorist group by Turkey, the US and EU.
However, the YPG is the main component in the Syrian Democratic Forces (SDF), an assortment of US-trained Kurdish and rebel militias who have driven the Islamic State group out of northern Syria.
Turkey has taken part in two major operations in northern Syria since the start Kurdish forces took control of border areas.
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Operation Euphrates Shield in 2016 saw Turkish-backed rebels win back key towns and cities in northern Syria from IS, and limited the spread of SDF-controlled territories after they also took part in an offensive against the jihadi group.
An operation against the YPG in Afrin earlier this year also saw Turkish-backed rebels take hold of key border areas in north-west Syria.
Turkey also operates a number of observation posts in rebel-controlled Idlib province.
Earlier on Monday, Turkey's Interior Minister Suleyman Soylu told reporters it would take whatever action necessary to protect its borders from Kurdish militias.
"[The US] has tried to confine us in northern Iraq, it tried to confine us in Afrin. And now, it will try to confine us east of the Euphrates. Turkey did not let it happen back then and we will not let it happen this time," Soylu said.
US backing for Kurdish forces in Syria has been a key point of contention between Washington and Ankara.
Relations between the two countries improved following the release of American pastor Andrew Brunson, although Ankara has still insisted on the YPG militias being cleared from the border area.
Turkish shelling on YPG posts in northern Syria led to the SDF halting operations against IS in a pocket of territory they still control in the east of the country.
The PKK has fought a decades-long insurgency against Turkey, carrying out attacks on military and civilian targets in a bid for greater political autonomy for Kurds in the country's south-east.
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