The three sons of murdered Maltese journalist Daphne Caruana Galizia have demanded the resignation of the country’s prime minister, as it emerged that the car bomb that killed her was probably triggered by a mobile phone signal.

Investigators believe the bomber would have had visual contact with Mrs Caruana Galizia’s car as she left her home in the village of Bidnija on Monday.

The bomber appears to have waited until the Peugeot was clear of other houses before detonating the device, which investigators believe was packed with Semtex, the plastic explosive that brought down Pan Am Flight 103 over Lockerbie in Scotland in 1988, killing 270 people.

Analysis of mobile phone calls may enable investigators to pin-point the bomber's location when the device was detonated.

Scotland Yard denied media reports that British detectives were set to fly to Malta to help with the investigation.

Investigators have reportedly found the mangled remains of the journalist’s laptop in the wreckage of her car, as well as remains of the bomb.