'Surrender and face no harm,' US-backed alliance tells IS

A Kurdish-Arab alliance battling the Islamic State group in Syria has vowed that jihadis could still lay down their arms and evade persecution.

The US-backed Syrian Democratic Forces said on Thursday that IS fighters have until the end of May to surrender and not face harm, as the alliance pushed closer to the extremists' de-facto Syrian capital of Raqqa, Reuters reported.

"This will allow the greatest number possible of those who were deceived or forced to join to benefit from this opportunity," Jihane Sheikh Ahmad, SDF spokeswoman, said in a statement.

Ahmad said that a ten day amnesty period earlier this month has been extended until the end of the month after it had produced "positive results".

She promised that the SDF would not harm the militants who surrendered regardless of their position within IS.

As of Wednesday, the SDF were only three kilometres from Raqqa at their closest point to the east, making the city visible to the naked eye for the first time since the offensive began in November.

The SDF seized a village five kilometres east of Raqqa city on Wednesday following three days of clashes with IS militants.

They have closed in on Raqqa from the east, south east and north, taking back from IS the strategic Tabqa town and its dam to the west of Raqqa.

Earlier this month, The SDF said they would launch their final assault on Raqqa in early summer - mostly likely in June.

Around 3,000 to 4,000 IS fighters are thought to be holed up in Raqqa, where they continue to erect defences against the anticipated assault.

The US has announced it will arm the Kurdish elements of the SDF for the fight for Raqqa - dubbed Operation Wrath of the Euphrates.

The SDF is dominated by the Kurdish People's Protection Units [YPG], seen by the US as an indispensable ally in the fight against IS but considered a "terrorist group" by Turkey.