US will step up air strikes to 'annihilate' Isis and citizen casualties are inevitable, warns Defence Secretary

Pentagon chief James Mattis has said that the US is “accelerating the tempo” of the fight against Isis, and that civilian deaths should be anticipated as a “fact of life”.

While US forces operating in Syria and Iraq do “do everything humanly possible” to prevent the loss of innocent life, “Civilian casualties are a fact of life in this sort of situation,“ General Mattis told CBS’ Face the Nation on Sunday.

The battle has already shifted from attrition to “annihilation tactics,” he said, designed to prevent foreigners who joined the so-called caliphate from returning home.

The interview comes after new figures from war monitor the Syrian Observatory for Human Rights found that the last four-week period was the deadliest for Syrian civilians on record since the US-led coalition bombing campaign began in 2014.

A total of 225 civilians, including 36 women and 44 children, were killed in the period between 23 April to 23 May, the UK-based Observatory said.

The Western coalition strikes are conducted without the consent of the Syrian government, with which the US does not have official diplomatic ties, and have long been criticised by Damascus and Syria’s allies in Moscow and Tehran for causing unnecessary loss of life.

However, since US President Donald Trump entered office in January this year there has been a marked uptick in civilian deaths in bombing operations against Isis across both Syria and neighbouring Iraq.

Mr Mattis said on Sunday that Mr Trump had given the Pentagon greater executive control over military operations against Isis, as per his election trail promises to focus his foreign policy on eliminating the group.

“Probably the most important thing we're doing now is we're accelerating this fight,” he said. “We're accelerating the tempo of it....

“We are going to squash the enemy's ability to give some indication that they're - that they have invulnerability, that they can exist, that they can send people off to Istanbul, to Belgium, to Great Britain and kill people with impunity,” General Mattis added.

In March, the US was accused of killing around 300 civilians alone after one strike which hit a mosque in Aleppo province and two incidents in the fight for Isis-controlled neighbourhoods of the Iraqi city of Mosul.

Last week the US admitted at least 105 Iraqi civilians were killed in one of the Mosul strikes. Investigations into all three incidents are still underway.

An official US military estimate from earlier this month found that 352 civilians in total have been unintentionally killed since the campaign began - but rights groups have severely criticised the estimate as too low, accusing the US of not taking “sufficient precautions” to avoid civilian deaths.

Isis now holds onto just a fraction of the territory that was under its control at the height of the group’s powers in 2014.

Twin US-backed campaigns to oust fighters from their last urban strongholds - Raqqa in Syria and Mosul in Iraq - are underway, led by local forces on the ground and assisted by US military advisors and aerial campaigns.

The complex Syrian civil war has killed almost 500,000 people, the UN says, and is now in its seventh year.