If the promises are kept until Tuesday, the safe zone issue will be resolved, said Tayyip Erdogan.

Turkish President Recep Tayyip Erdogan Friday warned that Ankara would restart its operation against Kurdish forces in Syria on Tuesday evening if they did not withdraw from a "safe zone".

Turkey has agreed to suspend its offensive for five days in northern Syria while Kurdish fighters withdraw from the area, after high stake talks with US Vice President Mike Pence in Ankara.

"If the promises are kept until Tuesday evening, the safe zone issue will be resolved. If it fails, the operation... will start the minute 120 hours are over," Erdogan told reporters during a foreign media briefing in Istanbul.

He said Turkish armed forces would remain in the region "because the security there requires this", adding that the agreement was holding and there had been no issues so far.

But the Syrian Observatory for Human Rights said Friday there had been Turkish air strikes on the village of Bab al-Kheir, east of Ras al-Ain on the border. The war monitor said 14 civilians were killed.

Turkey launched the cross-border incursion on October 9 after repeatedly threatening to clear the border area from the Kurdish People's Protection Units (YPG) militia.

The Turkish forces are supporting Syrian rebel fighters under the "Syrian National Army" banner but the proxies have been accused by Amnesty International of committing "war crimes" including summary executions.

Erdogan also condemned the abuses that some Syrian proxies are accused of having committed during the offensive.

"Whoever commits such an act is no different from (the ISIS). We cannot accept such a thing," he said, adding that the army was investigating the claims.

Kurdish authorities in northeastern Syria also accused Turkey of resorting to banned weapons such as napalm and white phosphorus munitions, a charge Erdogan denied.

"There are certainly no chemical weapons in the inventory of our armed forces. This is all slander against our armed forces," he added.

He accused the YPG of freeing nearly 750 ISIS terrorists including 150 Turks but said 195 of them had been caught.

Erdogan said Ankara was not bothered by the Syrian regime's control of the areas cleared from the Kurdish fighters.

"The regime's control is not a source of concern to us. What matters to us is that terror groups leave the safe zone."

'No intention to stay'

While US President Donald Trump appeared to initially greenlight the offensive, he made repeated threats against Turkey, often in tweets, following international outrage.

He then sent Pence and the US Secretary of State Mike Pompeo with other US officials to Ankara to thrash out a deal, which was announced on Thursday after hours of talks.

Erdogan said the proposed "safe zone" would be 32 kilometres (20 miles) deep, and 444 kilometres in length, and patrolled by Turkey.

He added that the region between the border towns of Tal Abyad and Ras al-Ain had been cleared, "but this is not over. The process is ongoing".

Pointing to a map, he said 12 observation posts would be set up to monitor the zone.

But, he said, "We have no intention to stay there. This is out of the question."

Just hours before the US-Turkey talks, a letter seen by many as bizarre appeared in the US media from Trump to Erdogan, in which the US leader urged Erdogan not to be a "fool" and warned his Turkish counterpart that history risked branding him a "devil."

Erdogan said Friday the letter was not in line with "political and diplomatic courtesy... but our mutual love and respect does not allow us to keep it on the agenda".

He also said he hoped the deal would become a "milestone" and "new begining" in Turkish-US relations fraught by a series of issues including American support for the Kurdish terrorists in Syria.