PARIS (Reuters) - French authorities put four members of a family in police custody on Wednesday as part of a preliminary investigation in connection with a plot to carry out an attack, a judicial source said.

The four were arrested in the Clichy-sous-Bois suburb, east of the capital.

Bomb-making materials, including acetone and sulphuric acid, which can be used to make explosives, were found in a building in the neighborhood in January.

DNA traces from the objects led police to the suspects, who were arrested on Tuesday, the source said.

France is under heightened alert following a spate of attacks by Islamist militants in several cities that has killed around 230 people since January 2015.