The US military confirmed Thursday that an extra 400 US troops have been deployed to Syria, including Marines who will support a major offensive to recapture al-Raqqa, Deash's de-facto capital in the country.
A spokesman for US Central Command in Tampa, Florida, also told dpa Army Rangers had been deployed to the northern Syrian city of Manbij to prevent any further fighting there.
The 400 troops were being deployed for a limited time and are in addition to 500 US troops already in Syria, the spokesman said.
The deployment of the Marines, which was first reported on Wednesday, will provide additional capabilities that allow the coalition to provide "flexible all-weather fire support to our Syrian partners when they need it most," Pentagon spokesman Major JT Rankine-Galloway told dpa earlier Thursday in an email.
"Our partners in Syria face an entrenched foe and like the Iraqis, will require additional support to enable them to fight and defeat (Deash) in Raqqa," Rankine-Galloway said.
A Kurdish-led alliance, backed by the United States, began a major offensive in November to recapture al-Raqqa, which has been under Daesh rule since 2014.
It is accompanied by a US-led campaign targeting militants that started fighting in war-torn Syria in September 2014.
A series of airstrikes Thursday on two areas controlled by the Daesh in Syria killed at least 30 civilians, according to the Syrian Observatory for Human Rights, a monitoring group.
Twenty-three were killed in a bombardment by suspected US-led coalition jets on the village of al-Matab on the eastern outskirts of al-Raqqa.
A further seven civilians died when aircraft - believed to be Russian - carried out some 25 strikes Thursday on the area of al-Mayadeen east of Deir al-Zour, the Observatory said.
The strikes hit a local school, bakery and a municipality building, leaving at least 70 injured, the watchdog added.
Al-Matab village lies near a key road linking al-Raqqa in north-eastern Syria with the city of Deir al-Zour in the east. The fatalities there included eight children.
"Most of those killed were from one family," Observatory head Rami Abdel-Rahman said.
At least 890 civilians have been killed in a US-led campaign targeting militants who started fighting in war-torn Syria in September 2014, according to the observatory.
In recent months, the jihadist group has been the target of multiple campaigns in Syria.
Regime forces, backed by allied Russian jets, on Thursday entered the al-Jarah military airport on the eastern edge of the northern province of Aleppo after Islamic State fighters had fled the facility to al-Raqqa, the Observatory said.
In recent weeks, government forces have wrested back several villages in Aleppo from Daesh as part of a Russia-backed onslaught.
Earlier this week, the Syrian Democratic Forces - an alliance of Kurds and Arabs that is currently encircling al-Raqqa - cut off a major road leading east of al-Jazzrah region on the north-western outskirts of al-Raqqa.
The route connects al-Raqqa with Deir al-Zour province. Daesh controls half of Deir al-Zour as well as most of the surrounding province of the same name.
On January 14, Daesh insurgents started a massive attack on areas still held by the regime in Deir al-Zour.
In recent months, Daesh has suffered military setbacks and lost territory in Syria and neighbouring Iraq.
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