Three members of Britain's special forces were injured in fighting with Islamic State gunmen in Iraq, the Mirror newspaper reported on Saturday without giving any details about its sources.
The Ministry of Defence said it did not comment on special forces operation.
The Mirror said the injured men were from the SAS and SBS units and were taking part in a 25-strong allied special forces patrol in northern Iraq when they came under fire by 30 Islamic State fighters in armoured Humvees stolen from the Iraqi army.
It said the covert patrol by British, German and US special forces aimed to identify Islamic State positions outside Mosul and spot weak areas in the militant group's defences.
The report said the Islamic State fighters involved in the incident were all killed as the special forces fought back with assault weapons and called in an air strike. The three men hit by shrapnel were treated on the ground before being airlifted out by helicopter, it said.
Britain is taking part in air strikes on Islamic State-held areas in Iraq and Syria and says it has troops present in Iraq providing training to Iraqi security forces.