The number of civilians killed by US airstrikes in Iraq and Syria is more than double the previous estimate, US Central Command said on Wednesday, after reexamining its air campaign based on allegations from activist groups.

The announcement of 64 additional deaths brings the total civilian death toll in US air attacks to 119 since the campaign against the Islamic State began in 2014, Centcom said. The command, responsible for US military operations in the Middle East, is investigating other allegations.

“Sometimes civilians bear the brunt of military action but we do all we can to minimise those occurrences, even at the cost of sometimes missing the chance to strike valid targets in real time,” Col. John Thomas, a Centcom spokesman, said in a statement.

Previously, Centcom had acknowledged only 55 deaths, the result of a lengthy investigative process that critics say has moved too slowly and has given inadequate weight to on-the-ground reports from local media, rights groups and activists. Some advocacy organisations, such as Amnesty International, have put the death toll much higher.

Centcom officials said they have been working in recent months to broaden the scope of their casualty investigations, seeking to compare information from military channels with that from external reports. Centcom has also introduced a new software program that seeks to reconcile that information and has in instances of conflicting death tolls chosen to use a higher estimate, a defense official said.

Chris Woods, director of Airwars, a Britain-based organisation that tracks allegations of civilian deaths in detail, said it was a positive sign that Centcom was incorporating external reporting into its oversight in a new way.

In its report, Centcom provided details of 24 separate incidents, roughly half in Syria and half in Iraq, in each of which military officials concluded at least one civilian was inadvertently struck. They included an April 9 strike in Mosul, the militant stronghold in northern Iraq, in which Centcom concluded that one civilian entered the target area after the US aircraft fired its weapon. Airwars’ examination of the incident, in contrast, said that as many as 67 people may have died.

In other incidents, the same explanation was provided for why a civilian was hit; in some cases, no explanation was offered.

Woods said the new list contained significant omissions, including a flurry of allegations that accompanied a major operation to reclaim the city of Manbij in northern Syria last summer.

One of those is a July 19 strike in the village of Tokhar, which activists said killed as many as 100 people. US military officials, speaking privately, described most of those as militants but said that about 10 civilians may have died. Centcom said that incident remains under investigation.

Even as Centcom acknowledges the civilian deaths, Thomas said US military officials had followed “the right processes” in each of the 24 incidents. “Significant precautions were taken, despite the unfortunate outcome,” he said.

While Centcom released redacted incident investigations early in its air campaign, it no longer does so. Officials at the command said that the documents might be obtained through Freedom of Information Act requests, even though such petitions can take years and often yield little useful information.

Woods said US allies taking part in the air war against Isis, which include Britain and France, must now improve their own transparency about potential civilian deaths.

British jets prepare for air strikes in Syria Show all 10 1 /10 British jets prepare for air strikes in Syria British jets prepare for air strikes in Syria A Tornado jet takes off from RAF Lossiemouth in Scotland, as RAF Tornado jets carried out the first British bombing runs over Syria British jets prepare for air strikes in Syria Pilots and ground crew prepare combat aircraft Panavia Tornados at RAF Marham at RAF Marham, UK Getty British jets prepare for air strikes in Syria A Eurofighter Typhoon jet takes off from RAF Lossiemouth in Scotland, as RAF Tornado jets carried out the first British bombing runs over Syria British jets prepare for air strikes in Syria A RAF Tornado arrives at RAF Akrotiri to begin operations in Akrotiri British jets prepare for air strikes in Syria A Tornado jet ahead of taking off from RAF Lossiemouth in Scotland, as RAF Tornado jets carried out the first British bombing runs over Syria, the Ministry of Defence has confirmed. The air strikes were carried out within hours of a vote by MPs in the Commons to back extending operations against Isis from neighbouring Iraq British jets prepare for air strikes in Syria Personnel work on a British Tornado after it returned from a mission at RAF Akrotiri in southern Cyprus British jets prepare for air strikes in Syria Two RAF Tornado GR4's, both with remaining weapons ordnance, approach RAF Akrotiri in Cyprus, as they return to the base after carrying out some of the first British bombing runs over Syria British jets prepare for air strikes in Syria A RAF Tornado takes off from RAF Akrotiri, on the Mediterranean island nation of Cyprus British jets prepare for air strikes in Syria A Tornado jet leaving RAF Lossiemouth in Scotland British jets prepare for air strikes in Syria AKA RAF Tornado arrives at RAF Akrotiri to begin operations in Akrotiri, Cyprus. The RAF has sent two further Tornado aircraft and six Typhoons to bolster aircraft now flying sorties to both Iraq and Syria

Centcom’s new list of casualty incidents is below:

November 20, 2015, near Dayr Az Zawr, Syria, against an ISIL tactical unit, it is assessed that five civilians were killed and three individuals were injured after the civilians entered the target area after the aircraft released its weapon.

March 5, 2016, near Mosul, Iraq, on a strike against an ISIL weapons production facility it is assessed that 10 civilians were killed.

March 24, 2016, near Qayyarah, Iraq, during a strike against an ISIL target, it is assessed that one civilian was killed.

April 1, 2016, near Ar Raqqah, Syria, against ISIL tactical unit, it is assessed that three civilians were killed after entering the target area after the aircraft released its weapon.

April 9, 2016, near Mosul, Iraq, during a strike against an ISIL tactical unit, it is assessed that one civilian was killed after entering the target area after the aircraft released its weapon.

April 30, 2016, near Mosul, Iraq, against ISIL military leadership, it is assessed that five civilians were killed after entering the target area after the aircraft released its weapon.

May 25, 2016, near Mosul, Iraq, during a strike against an ISIL tactical unit, it is assessed that one civilian was killed.

May 26, 2016, near Mosul, Iraq, during a strike against ISIL fighters, it is assessed that one civilian was killed after entering the target area after the aircraft released its weapon.

May 29, 2016, near Mosul, Iraq, during a strike against an ISIL weapons system, it is assessed that six civilians were killed.

June 15, 2016, near Kisik, Iraq, during a strike against an ISIL weapons storage facility, it is assessed that six civilians were killed.

June 15, 2016, near Mosul, Iraq, during another strike against ISIL targets, it is assessed that two individuals were injured after entering the target area after the aircraft released its weapon.

June 21, 2016, near Ar Raqqah, Syria, during a strike targeting an ISIL headquarters building, it is assessed that three individuals were killed after entering the target area after the aircraft released its weapon.

June 23, 2016, near Ar Raqqah, Syria, during a strike against an ISIL-held building, it is assessed that four civilians were killed after entering the target area after the aircraft released its weapon.

June 26, 2016, near Mosul, Iraq, during a strike against an ISIL target, it is assessed that one individual was injured after entering the target area after the aircraft released its weapon.

June 26, 2016, near Mosul, Iraq, during another strike against an ISIL target, it is assessed that one individual was injured after entering the target area after the aircraft released its weapon.

July 3, 2016, near Manbij, Syria, during a strike against an ISIL fighting position, it is assessed that four civilians were killed.

July 10, 2016, near Manbij, Syria, during a strike against an ISIL target, it is assessed that two civilians were killed.

July 14, 2016, near Qayyarah, Iraq, during a strike on an ISIL-held building, it is assessed that one civilian was killed.

July 31, 2016, near Manbij, Syria, during a strike against ISIL fighters, it is assessed that one civilian was injured after entering the target area after the aircraft released its weapon.

August 17, 2016, near Ar Raqqah, Syria, during a strike against an ISIL target, it is assessed that two civilians were killed.

August 20, 2016, near Manbij, Syria, during a strike against an ISIL artillery firing position, it is assessed that one civilian was killed after entering the target area after the aircraft released its weapon.

August 31, 2016, near Ramadi, Iraq, during a strike against an ISIL target, it is assessed that two civilians were killed.

September 7, 2016, near Dayz Az Zawr, Syria, during a strike against an ISIL oil collection point, it is assessed that one civilian was killed after entering the target area after the aircraft released its weapon.

September 10, 2016, near Ar Raqqah, Syria, during a strike against an ISIL target, it is assessed that five civilians were killed.