America and the UK condemned Russian airstrikes that killed or injured hundreds of civilians during last autumn’s siege of Aleppo, accusing Vladimir Putin of war crimes. The question now is whether the US, backed by British air power, is committing similar atrocities against civilians in Mosul.

Addressing the UN security council in September, Matthew Rycroft, Britain’s ambassador, said Russia had “unleashed a new hell” on Aleppo. “Russia is partnering with the Syrian regime to carry out war crimes,” he said. The US accused Putin of “barbarism”.

Theresa May climbed aboard this righteous bandwagon in December, joining Barack Obama and European leaders in lambasting Russia for causing a humanitarian disaster that “is taking place before our very eyes”.

Fast-forward to Mosul in northern Iraq last week, where misdirected US airstrikes caused a massive explosion that reportedly killed at least 150 civilians sheltering in a basement. The Americans say they were targeting Islamic State fighters. The Russians said much the same about Aleppo – that they were attacking jihadi terrorists. Many people, not least the relatives of the Mosul dead, will struggle to see the difference.

At least 150 civilians are believed to have died in Mosul. Photograph: Cengiz Yar

American spokesmen do not deny the US launched airstrikes in the Jadida neighbourhood of Mosul. As to who was responsible for the civilian casualties, “at the moment the answer is we don’t know”, Colonel John Thomas said.

But Iraqi commanders said the deaths followed an Iraqi army request for US air support to clear Isis snipers atop three buildings. They said they did not realise civilians were sheltering beneath, and it may have been a deliberate Isis trap.

Trap or not, the high death toll places the Mosul carnage, if confirmed, among the worst such incidents since the US invasion in 2003. It also serves to highlight a new pattern of behaviour by US forces since Donald Trump took office in January. Since then, the monthly total of recorded civilian deaths from coalition airstrikes in Iraq and Syria has more than doubled, according to independent monitors.

US spokesmen deny rules of engagement have changed. But the Mosul strike, and two similar, recent attacks in Syria, suggest Trump has fulfilled his campaign promise to let field commanders off the leash. According to the Syrian Observatory for Human Rights, 49 people were killed on 16 March by a US strike on a complex that included the Omar ibn al-Khattab mosque.

Last Tuesday at least 30 Syrian civilians died in another American airstrike, on Mansoura, in Raqqa province. The American planes hit a school. The raid was one of 19 coalition missions that day, ordered in preparation for the expected assault on the Isis headquarters in Raqqa city itself.

The president with his secretary of defence, Jim ‘Mad Dog’ Mattiss. Photograph: Erik S. Lesser/EPA

The pace and scale of fighting in Iraq and Syria is picking up as the US-led coalition scents final victory over Isis. Trump recently approved an expanded deployment of US ground forces in Syria. But human rights groups say increased combat intensity does not excuse or justify fatal carelessness with civilian lives. Such “own goals” hand propaganda victories to Isis and may also motivate its followers to commit terrorist acts.

Trump has frequently vowed to exterminate Isis by all means. It is one of his few clearly stated foreign policy aims. The White House accused Obama of micromanaging operations. Trump, in contrast, appears to have delegated most control to Jim “Mad Dog” Mattis, the former general appointed Pentagon chief.

The first results of Trump’s laissez-faire approach were seen in January when he authorised a special forces raid in Yemen over dinner. The attack on al-Qaida went disastrously wrong, causing dozens of civilian deaths and one US military fatality.

Now Iraq and Syria are bearing the brunt of Trump’s brash bellicosity. Putin will certainly be watching. It may not be long before the US president faces war crimes allegations, too. And what will May say then?