US-led coalition airstrikes targeting the Islamic State and other designated terrorist groups in Syria have killed 380 civilians, including 99 children and 67 women, over the past 18 months, according to the Syrian Observatory for Human Rights (SOHR).

The monitoring group said that it had documented these mortalities among a total of 4,643 deaths resulting from Operation Inherent Resolve, which the coalition launched on September 23, 2014 with a mission to "degrade and defeat" the Islamic State group in Syria and Iraq.

Among the civilians allegedly killed by airstrikes is a family of seven that died in the village of Dali Hasan and another 64 people in Bir Mahli. The attacks blamed for their deaths both took place in Aleppo Province on April 30, 2015.

SOHR says that the civilians killed in Bir Mahli included 31 children and 19 women.

The organization condemned the deaths, branding the coalition's bombing "a massacre" while calling for "neutralizing civilian's areas from all kinds of military operations, where the victims of these operations are the Syrian civilians."

The US military has admitted to killing just 21 civilians since Operation Inherent Resolve began.

Chris Davis, director of the website Airwars, which tracks and compiles data about airstrikes in Syria and Iraq, says that the number of deaths documented by SOHR is far too low. Airwars estimates that the US-led coalition has likely killed around 519 civilians in Syria alone.

"More than 1000 civilians have been killed by the coalition in Iraq and Syria, by everybody's count," he said, noting that, as of Wednesday, more than 11,000 bombs had been dropped onto both countries since the start of the operation.

With so many munitions falling onto populated areas occupied by Islamic State, Davis said, it's not surprising that hundreds of civilians have been killed — but he maintains that the coalition doesn't want to admit it due to the nature of the conflict.

"This is supposedly a war being fought on behalf of civilians in Iraq and Syria, and it's not helpful if you're killing civilians to achieve those goals," he remarked. "Every single casualty- assessing and tracking organization is coming back with the same message: hundreds of civilians have died in Iraq and Syria, and the coalition isn't taking it seriously enough."

A Defense Department spokesperson said that the Pentagon closely reviews all reports of civilian deaths in the course of its operations.

"We take all allegations of civilian casualties seriously, and we apply very rigorous standards in our targeting process to avoid or to minimize civilian casualties," said Major Roger M. Cabiness II. "We take great care — from analysis of available intelligence to selection of the appropriate weapon to meet mission requirements — to minimize the risk of collateral damage, particularly any potential harm to non-combatants."

In addition to the civilian deaths, SOHR said that it had documented the killing of 4,108 Islamic State militants and 136 Nusra Front fighters by the coalition.

"We believe that the real number of casualties on IS and the other factions' ranks is more than our documented number due to IS concealment on its casualties," the monitoring group said in a statement.

More than 250,000 people have died in Syria since the conflict there began in 2011, according to the United Nations.