US drone and airstrikes have killed at least 22,000 civilians – and perhaps as many as 48,000 – since the 9/11 terrorist attacks in 2001, according to new analysis published by the civilian harm monitoring group Airwars.

The analysis, based on the US military’s own assertion that it has conducted almost 100,000 airstrikes since 2001, represents an attempt to estimate the number of civilian deaths across the multiple conflicts that have comprised aspects of the “war on terror”.

The figures, released just ahead of the 20th anniversary of 9/11, come as the US president, Joe Biden, promised to end the “forever wars” that have marked the past two decades, and with the US withdrawal of troops from Afghanistan.

Since taking office Biden has reduced US reliance on airstrikes amid a formal review of US drone policy, and has withdrawn from many of the foreign interventions that marked the time in office of his three predecessors George W Bush, Barack Obama and Donald Trump, since the 2001 attacks on the US by al-Qaida.

Encompassing attacks on Islamic State in Syria, the conflicts in Iraq and Afghanistan, as well as strikes against militant and terror groups in Yemen, Somalia, Pakistan and Libya, the US has said it had conducted at least 91,340 strikes in 20 years – including 9,000 against the Islamic State, the Airwars report said.

Based on that total, Airwars has calculated that “US actions likely killed at least 22,679 civilians, with that number potentially as high as 48,308”.

According to the group’s research, the deadliest year in the past two decades for civilian victims of US airstrikes was 2003 when a minimum of 5,529 civilians were reported to have been killed, almost all during the invasion of Iraq that year.

The next deadliest year was 2017 when at least 4,931 civilians were likely killed, the vast majority in coalition bombing of Iraq and Syria.

However, going by the maximum estimates, 2017 emerges as the worst year for civilians, with up to 19,623 killed, almost all in the bombing campaign against IS.

The death toll from US airstrikes – which the group admits is imprecise – compares with an estimated 387,000 civilians who are believed to have been killed by all parties during the war on terror, according to work done by Brown University’s Costs of War Programme.

The issue of civilian casualties of western airstrikes and other military activities during the war on terror has always been highly contested territory, with the US and its allies insisting that strenuous efforts have been made to minimise civilian death and injury.

And despite the wide-ranging umbrella of operations that have encompassed the war on terror, the US – according to a statement issued by the Pentagon – has never sought to calculate a total of civilian deaths ascribed to actions under its aegis.

An email reply to Airwars from the Pentagon’s Central Command (Centcom) said that it did not have information available on the total number of civilian deaths from airstrikes.

“The information you request is not immediately on hand in our office as it spans between multiple operations/campaigns within a span of between 18 and 20 years,” Centcom said.