The man who rammed a car into a police van on Paris's Champs-Elysees pledged allegiance to the Islamic State group in a letter found by investigators, a source close to the probe said Tuesday.

The letter from Adam Djaziri, a 31-year-old who had been on a French watchlist for radical Islamists since 2015, was addressed to his brother-in-law and pledged allegiance to IS leader Abu Bakr al-Baghdadi, the source said.