Turkish soldiers at the Turkey-Syria border in 2014

TURKEY has said eight of its troops were killed in Ankara's military operation against a Syrian Kurdish militia, the deadliest day in the two-week-old offensive in the enclave of Afrin.

In a statement late on Saturday, the Turkish military said five soldiers were killed after their tank in Syria came under attack near Afrin. The soldiers could not be saved despite all attempts, it said.

Earlier in the day, three Turkish soldiers were reported killed in the Afrin offensive – one was killed in the area of the tank attack, another in northern Syria and the third on the Turkish side of the border in what Ankara said was an attack by Syrian Kurdish militiamen.

The total death toll for Turkish troops since the operation, codenamed Olive Branch, started on January 20 now stands at 13.

Turkey launched the incursion into Afrin to rout the US-backed Syrian Kurdish militia, known as the People's Protection Units (YPG), which it considers to be a terrorist organisation and an extension of Kurdish insurgents fighting within Turkey.

From Istanbul, Turkish presidential spokesman, Ibrahim Kalin, said Turkey will not tolerate the presence of the YPG "anywhere" along its southern border, hinting that Ankara might expand the Afrin operation eastward.

Turkey's first demand is to see the YPG move east of the Euphrates River and leave the town of Manbij, where American troops backing the Syrian Kurdish fighters are stationed, Mr Kalin said.

He called on the United States to "disengage" from the YPG and said Turkey will continue communications with "our American allies to avoid any confrontation".

Turkey shares a 911km border with Syria. The YPG controls much of the territory along the border and an uninterrupted strip from Manbij to the Iraqi border.

Meanwhile, in the embattled northwestern province of Idlib, al Qaida-linked militants said they downed a Russian fighter jet and killed its pilot after he ejected from the plane and landed on the ground.

The pilot resisted being captured and fired at the militants who then shot and killed him, according to one of the militants and Syrian monitors.

The Russian Defence Ministry confirmed the downing of the Su-25 and said the pilot was killed in fighting with "terrorists". A report on the ministry's Zvezda TV said preliminary information indicated the plane was shot by a portable ground-to-air missile in an area under control of al Qaida's branch in Syria.

The Britain-based Syrian Observatory for Human Rights said the plane was downed near the rebel-held town of Saraqeb, which Syrian troops have been trying to take under the cover of Russian airstrikes.

Russia is a key ally of President Bashar Assad, and has been waging a military campaign on behalf of his forces since 2015. Since then, Syrian troops have captured wide parts of the country and in recent weeks have been making advances in Idlib. The province is also a base for al Qaida's branch in Syria and other Islamic groups.

Also Saturday, Syria's Foreign Ministry has dismissed as "null and void" US accusations that Assad's government is producing and using "new kinds of weapons" to deliver deadly chemicals despite committing to abolish its program in 2013.

The American statements are "nothing more than lies" based on accounts of what the Trump administration called its partners on ground, the ministry said. It also said reports by Western-backed media outlets about Damascus using chemical weapons were "a new version of US and Western desperate intentions to create" an excuses to attack Syria.

President Donald Trump has not ruled out additional military action to deter attacks or punish Assad, administration officials said earlier this week, although they did not suggest any action was imminent.