Donald Trump’s decision to let the US military off the leash in the fight against Islamic State and like-minded terror groups in combat zones in the Middle East and north Africa appears to be a significant contributory factor in a sharp, across-the-board rise in civilian casualties reported by the UN and aid agencies.

This week the US president handed over direction of the war in Afghanistan to his defence secretary, the former Marine Corps general, Jim Mattis. It was the latest in a series of similar moves effectively giving Pentagon chiefs a free rein in Syria, Iraq, Yemen and Somalia.

The hands-off policy is raising fears about unchecked battlefield escalation and a lack of democratic oversight of the US military machine, as well as an increased civilian toll. At the same time, Trump stands accused of failing to develop or pursue credible peace-making strategies. Mattis already has authority to direct operations in Syria and Iraq.

In both theatres direct US involvement on the ground and in the air has grown since January, when Trump took power. There has been a marked rise in civilian casualties in the same period, notably in besieged, Isis-held Raqqa and Mosul, according to aid agencies and monitors.

On Wednesday the UN reported a “staggering” loss of life from US-led coalition air strikes in Raqqa. The implication is that war crimes may have been committed by combatants on all sides. Isis has reportedly used civilians as human shields in both cities and is accused of many other abuses of the local populations.

Official US casualty estimates are invariably conservative and the UN gave no figures on Wednesday. Airwars, a UK-based watchdog group, recently estimated this year’s civilian death toll from coalition airstrikes in Iraq and Syria at over 3,800.

Trump’s hand-over to Mattis suggests force levels in Afghanistan will soon begin to rise again. In February, the US commander of international forces in Kabul, Gen John Nicholson, warned of a stalemate and requested up to 5,000 reinforcements. Nato countries, including Britain, have since been asked to contribute.

Testifying to Congress this week, Mattis said a Taliban “surge” was reducing territory under Afghan government control. “We are not winning in Afghanistan right now and we will correct this as soon as possible.” he said. But US objectives are uncertain – as Republican senator John McCain noted on Tuesday. The White House says a review of Afghan policy will be completed in July, but reports suggest it has expanded into a wider discussion about what to do about the Pakistani Taliban and Isis fighters in Afghanistan.

A devastating truck bomb in Kabul last month that killed more than 150 people, and ensuing violent, anti-government protests, have highlighted the deteriorating security situation.

Trump’s order to drop the US’s biggest non-nuclear bomb, a GBU-43, on Isis militants in rural Afghanistan in April now looks like a primarily symbolic show of force that disregarded the possible impact on civilians. His impetuous cruise missile attack on a Syrian government airfield, also in April, was another one-off. The president’s attention has since moved elsewhere.

The apparent effort by Trump, who campaigned on an “America First” platform, to distance himself from both life-and-death decision-making and the policy debate over broader strategic objectives has also raised questions about his personal political accountability. In office for only a few days, Trump had his fingers burned in January when he authorised a high-risk special forces operation in Yemen. The raid went disastrously wrong, leading to the death of one US serviceman and many civilians. Trump’s reaction was to deny responsibility and blame the military.

Trump’s approach contrasts with that of his predecessor, Barack Obama, who kept tight control over even small-scale military operations. Obama ended US involvement in the war in Iraq and eventually de-escalated in Afghanistan, cutting US troop numbers from about 100,000 to the current level of 8-9,000.

Trump, who has sought an “historic” increase in the Pentagon’s annual budget to $603bn, has also expanded counter-terrorism operations in Somalia and Yemen, with drone strikes on the rise. Increased US interventionism may have the opposite effect to that intended, with fighting spreading this month to Somalia’s north-eastern Puntland region.

Supporters say Trump’s hands-off approach allows the military to make quicker, smarter decisions. But observers with longer memories recall what happened when transparent political control over the military slipped in the Vietnam era and during Donald Rumsfeld’s time at the Pentagon following the 9/11 attacks.