PARIS (AFP, REUTERS) - Four people including a 16-year-old girl were arrested on Friday (Feb 10) by anti-terrorist police in Montpellier in southern France on suspicion of preparing an attack, a police source said.

"The four suspects were arrested after they bought acetone," the source told AFP, referring to a highly-explosive liquid that can be used to make bombs.

Reuters, citing police and justice sources, reported that the 16-year-old in custody was the girlfriend of a 22 year-old man, who has also been detained. The pair had been known to authorites for connections with radical Islam.

France remains on high alert over possible Islamist militant attacks. More than 230 people have died in a series of assaults since the beginning of 2015 and the country has been under state of emergency rules since November the same year.