The US-led international coalition fighting the Islamic State group said Wednesday it had conducted 18 air strikes near the strategic town of Manbij in northern Syria, opening a new front against the jihadists.

The announcement of the strikes followed word from the Syrian Observatory for Human Rights that US backed Kurdish and Arab fighters had thrust into the key jihadist-held pocket along the Turkish border.

"The offensive is on" to take Manbij, said a US defense official, who asked not to be identified.

"We are moving in" on Manbij, the official said, calling the city "the next target of the coalition" in its drive to expel the jihadists from Syria.

Strikes over the past 24 hours destroyed an IS headquarters, communication towers, six IS-used bridges and eight IS fighting positions, among other targets, according to a coalition statement sent out by Centcom.

IS-held Manbij is located in Aleppo province, some 20 miles (30 kilometers) west of the Euphrates.

The swath of territory controlled by IS on either side of the Euphrates River has long been a key target for Washington as it is seen as the main entry point for foreign fighters.

"The destruction of ISIL targets in Syria and Iraq further limits the group's ability to project terror and conduct operations," said the statement, using an alternate acronym for the IS jihadists.

The Pentagon has deployed more than 200 special forces troops alongside the Syrian Democratic Forces (SDF), a Kurdish-led alliance in which it has been trying to boost the Arab element.

SDF military adviser Nasser Haj Mansour told AFP earlier that the alliance's fighters were heading from the Tishreen Dam on the Euphrates towards Manbij.

"The clashes are fierce and intense," he said.

The offensive is one of two the SDF has launched against IS in northern Syria in recent weeks.

Last month, the alliance launched an assault on the jihadists north of their de facto Syria capital Raqa, seizing dozens of villages in the north of Raqa province.

Washington sees the SDF — which is dominated by the Kurdish People's Protection Units (YPG) — as the most effective ground force against IS in Syria.

With the help of coalition air strikes, the SDF has cleared IS jihadists from large parts of Syria's northeast.

But US support for the Kurdish-led alliance has angered NATO ally Turkey.

Ankara regards the YPG as a branch of the rebel Kurdistan Worker's Party (PKK), which has fought a three decade insurgency against the Turkish state.

The American defense official insisted however that the offensive is "Arab-led," and that "less than 20 percent of the fighters engaged in the fight are YPG."

Another US military official said YPG taking part in the fight "will return to their traditional" zone of influence once the city is conquered.

Air strikes in north Syria kill at least 42 civilians: monitor
Beirut (AFP) June 1, 2016 –

At least 42 civilians including five children were killed in regime, Russian and US-led coalition air strikes in northern Syria on Wednesday, a monitor said.

Regime air strikes killed 15 civilians in Idlib province, while Russian and regime air strikes killed at least 11 civilians in neighbouring Aleppo province, said the Syrian Observatory for Human Rights.

Seven of those died in regime raids on a bus on the Castello road, a key supply route for the rebels out of the divided provincial capital of Aleppo city, Observatory chief Rami Abdel Rahman said.

Air strikes by the US-led coalition killed a further six civilians in Aleppo's Manbij town and 10 in Raqa city in the province of the same name, both held by the Islamic State jihadist group, he said.

The international coalition fighting IS on Wednesday said it had conducted 18 air strikes near Manbij, which is located some 20 miles (30 kilometres) west of the Euphrates river.

Last week, a US-backed Kurdish and Arab alliance launched an assault on IS north of their de facto Syria capital Raqa, seizing dozens of villages in the north of the Raqa province.

At least 280,000 people have been killed and millions displaced since the Syria war started with the brutal repression of anti-government protests in 2011.