Turkey's president has threatened to resume an offensive in north-east Syria unless Kurdish fighters withdraw from the border before a ceasefire ends. Up to 1,300 People's Protection Units (YPG) militia members still had to pull back before 22:00 (19:00 GMT) on Tuesday, Recep Tayyip Erdogan warned. Turkish troops and allied Syrian rebels attacked on 9 October to set up a 32km (20-mile) deep "safe zone" in Syria. Mr Erdogan agreed to pause the assault last week at the request of the US. A US-led multinational coalition relied on the YPG to battle Islamic State (IS) militants in Syria over the past four years, but the Turkish government views it as a terrorist organisation with links to a Kurdish rebel group fighting in Turkey. The offensive began after President Donald Trump ordered US troops to leave the border area - a decision that was widely criticised by US lawmakers. The UN says more than 176,000 people, including almost 80,000 children, have been displaced in the past two weeks in north-east Syria, which is home to some 3 million people. Some 120 civilians have been killed in the battle, along with 259 Kurdish fighters, 196 Turkish-backed Syrian rebels and seven Turkish soldiers, according to the Syrian Observatory for Human Rights (SOHR), a UK-based monitoring group. Twenty civilians have also been killed in attacks by the YPG on Turkish territory, Turkish officials say. On Thursday, US Vice-President Mike Pence persuaded Mr Erdogan to agree to pause the Turkish offensive for 120 hours to allow the US to "facilitate the withdrawal of YPG forces from the Turkish-controlled safe zone". He also agreed to a permanent ceasefire upon completion of the YPG withdrawal. Since then the ceasefire has largely held, despite what US officials have described as "some minor skirmishes". On Tuesday, Mr Erdogan told reporters in Ankara that the withdrawal of YPG fighters from the border area was "continuing". "According to the information I have received from my defence minister, we are talking about 700 to 800 already withdrawn and the rest, around 1,200 to 1,300, are continuing to withdraw. It has been said that they will withdraw," he said. Mr Erdogan then warned that all the YPG fighters would have to "get out" by Tuesday night or the Turkish offensive would resume. "If the promises given to us by America are not kept, we will continue our operation from where it left off, this time with a much bigger determination." The president added that the YPG "does not have a place in the future of Syria" and that he would seek to end its presence in areas of Syria controlled by the Syrian government, which Turkey opposes. The Turkish president has said he wants the "safe zone" to cover all 440km of the Turkey-Syria border currently controlled by a militia alliance led by the YPG, called the Syrian Democratic Forces (SDF). But a Turkish security source told Reuters news agency the YPG was expected to withdraw initially from a 120km strip from Ras al-Ain to Tal Abyad. Turkish-led forces have seized control of both towns and large parts of the sparsely populated, mostly Arab area between them. The source said Mr Erdogan would discuss the YPG's withdrawal from the rest of the border during talks with Russian President Vladimir Putin in Sochi on Tuesday. Russian forces have been taking up many of the positions abandoned by YPG fighters and US troops near the border as part of an agreement Moscow brokered between Syrian President Bashar al-Assad's government, its ally, and the local Kurdish-led administration, which wanted help to halt the Turkish advance. The Russian deployment has created the potential for clashes between Russia and Turkey - something Mr Erdogan and Mr Putin want to avoid. "Russia wants to discuss the situation in the north-east of Syria, better understand what is going on," said Kremlin spokesman Dmitry Peskov before the Sochi meeting. "We want to acquire information about Turkey's plans and see how it compares with the general plan of the political settlement." Earlier on Tuesday, Russian military helicopters landed at the Tabqa airbase after US troops left, Russian defence ministry-controlled Zvezda TV reported.