At least 100 civilians have been killed over the past 48 hours by US-led air attacks targeting fighters in Raqqa, the de-facto capital of the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) in Syria.

Residents told Al Jazeera on Tuesday that at least 100 civilians had been killed since Sunday, with 55 civilians killed in the eastern neighbourhoods of Bedou and al-Sukhani on Monday.

Meanwhile, the UK-based Syrian Observatory for Human Rights (SOHR) put Monday's death toll at 42, including 19 children and 12 women, and said 27 were killed on Sunday - a two-day total of 69 people.

The deaths came on the second consecutive day of a ferocious bombing campaign in Raqqa, more than half of which has been captured by the US-backed Syrian Democratic Forces (SDF) battling ISIL.

"The tolls are high because the air strikes are hitting neighbourhoods in the city centre that are densely packed with civilians," SOHR director Rami Abdel Rahman told the AFP news agency.

"There are buildings full of civilians that are trying to get away from the front lines.

"Coalition air strikes are targeting any building where any kind of [ISIL] movements are being detected."

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Earlier this month, the aid group Doctors Without Borders (known by its French acronym, MSF) reported that food and medicine needed to treat the wounded were in short supply.

"In Raqqa city, if you don't die from air strikes, you die by mortar fire; if not by mortars then by sniper shots; if not by snipers, then by an explosive device," MSF said, quoting a 41-year-old who fled Raqqa after losing seven family members in the fighting.

"And if you get to live, you are besieged by hunger and thirst, as there is no food, no water, no electricity."

Thousands trapped

The US-led coalition, which operates in both Syria and neighbouring Iraq, says it takes all possible measures to avoid civilian casualties.

In August, it acknowledged the deaths of 624 civilians in its attacks in Syria and Iraq since 2014, but rights groups say the number is much higher.

The United Nations estimates there are up to 25,000 civilians trapped inside the city, with food and fuel supplies short and prohibitively expensive.

The UN's humanitarian point man for Syria, Jan Egeland, has said ISIL-held territory in Raqqa city is now "the worst place" in the war-torn country.

The Syrian conflict, which began with peaceful protests in March 2011 against President Bashar al-Assad, has spiralled into a multi-sided civil war.

The death toll stands at more than 400,000 people killed, according to UN estimates.