The powerful explosive Semtex is believed to have been used in the car bomb attack that killed Malta’s best-known investigative journalist.

The power of the blast, and the way in which the explosion happened, suggest that the plastic explosive, favoured by terrorist organisations such as the IRA for large-scale attacks, may have been used, according to police sources quoted by The Times of Malta.

Daphne Caruana Galizia, 53, who for years had accused Malta’s political elite of cronyism and corruption, was killed on Monday shortly after leaving her home. If confirmed, it would be the first time that Semtex has been used on the Mediterranean island.

A witness to the attack, a local man called Frans Sant, said he heard an initial, small explosion, which could have been the device’s detonator, followed by a much more powerful blast, which would have been the main charge.

Mrs Caruana Galizia had made a number of accusations of financial impropriety against Malta’s political elite, including the prime minister, Joseph Muscat.