An explosive belt has been found in the southern Paris suburb of Montrouge, French police said.

An official said the belt - without a detonator - was found by a street cleaner in a pile of rubble.

The vest was found near the place where a suspect's mobile phone was discovered.

It raised the possibility that he aborted his mission, either ditching a malfunctioning vest - or fleeing in fear.

The discovery of the vest in a Paris suburb came as Belgium's prime minister cited a "serious and imminent" threat justifying keeping the highest alert level operational for at least another week.

The security measures, already in place for three days, have severely disrupted normal life in the capital.

In France, police said the explosive vest - without a detonator - was found in a pile of rubble in Chatillon-Montrouge, on the southern edge of Paris, some distance from the sites of the attacks.

A police official said the vest contained bolts and the same type of explosives - TATP - as those used in the November 13 attacks that claimed 130 lives and left hundreds wounded.

The device was found on Monday in the same area where a mobile phone belonging to fugitive suspect Salah Abdeslam was located on the day of the Paris attacks.

But the vest has not been formally linked to him, police officials said.

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