Four people have been arrested and an attack plan foiled, French media are reporting.

Three men and a woman were detained at dawn in the 18th arrondissement of Paris and the nearby northern suburb of Seine-Saint-Denis, TF1 and BFMTV say.

They are reported to have been known to anti-terrorism officials who feared they were becoming a serious threat.

The French capital remains on high alert after the jihadist attacks in November which killed 130 people.

In the meantime, Belgian police were hunting for two suspects who fled an apartment linked to the Nov. 13 attacks in Paris, after a police sniper killed a third man and uncovered weapons, ammunition and an Islamic State flag. Four police officers were injured in the dawn raid.