At least 106 civilians, including 42 children, were killed in a series of airstrikes carried out by the US-led coalition on an Islamic State-held town in Syria, a monitor reported today.

The report came just hours after the United Nations accused the military alliance of failing to protect civilians in the war-torn country.The Syrian Observatory for Human Rights said the latest strikes targeted the town of al-Mayadeen on the eastern outskirts of the eastern province of Deir al-Zour.

"There were two rounds of strikes: one yesterday night and the second after midnight, targeting buildings housing families of Islamic State fighters," the Observatory''s head, Rami Abdel-Rahman, told dpa.

He added that most of those killed were Moroccan and Syrian nationals, who had fled to al-Mayadeen from al-Raqqa, the de facto capital of Islamic State in north-eastern Syria.

"This is a big massacre committed against families of the Islamic State fighters," Abdel-Rahman said.

Initially, the watchdog said at least 35 civilians had been killed in the strikes in al-Mayadeen. The latest coalition bombing targeted the town's municipality building and reduced it to rubble, according to the Britain-based Observatory, which relies on a network of activists inside Syria.

No comment from US-led alliance

There was no comment from the US-led alliance. The Observatory this week reported that between April 23 and May 23 of this year, coalition strikes had killed a total of 225 civilians in Syria.

Earlier today, the UN said the US-led alliance is not taking adequate care to prevent civilian deaths in Syria as it fights Islamic State extremists there.

"The same civilians, who are suffering indiscriminate shelling and summary executions by ISIL (Islamic State), are also falling victim to the escalating airstrikes," UN Human Rights chief Zeid Ra'ad Al Hussein said, pointing to mounting fatalities.

Civilian casualties have been particularly high in Deir al-Zour. Zeid also cited an airstrike that killed 23 farm workers, including 17 women, on May 14. On the following day, air attacks on the Islamic State-controlled city of Albo Kamal near the Syrian-Iraq border killed 59 civilians.

"Civilians should always be protected, whether they are in areas controlled by ISIL or by any other party," Zeid said in Geneva.

In addition, Islamic State militants have been killing people in these areas on suspicion that they have provided target coordinates for US-led strikes, Zeid said.

The raids on Deir al-Zour, which is mainly controlled by the hardline Sunni militia, came as the US-backed Syrian Democratic Forces (SDF), an alliance of Syrian Kurds and Arabs, continue to press ahead with a multi-pronged attack on al-Raqqa.

In November, the SDF started a major offensive aimed at capturing al-Raqqa, which has been under Islamic State-control since 2014. The US-led coalition air campaign against Islamic State in Syria began in September 2014.

- dpa