PARIS -

A street cleaner yesterday found an explosive vest similar to those used in the Paris attacks near the place where a fugitive suspect's cellphone was found, raising the possibility that he aborted his mission, either ditching a malfunctioning vest or fleeing in fear.

Authorities said the device, which did not have a detonator, was found in a pile of rubble in the southern Paris suburb of Montrouge. A police official said the vest contained bolts and the same type of explosive used in the Nov. 13 Paris attacks that claimed 130 lives and left hundreds wounded.

It was found in the same area where a cellphone belonging to fugitive suspect Salah Abdeslam was pinpointed by GPS on the day of the Paris attacks, two police officials said. The officials spoke on condition of anonymity because they were not authorized to discuss the investigation.

Police have been conducting a manhunt for Abdeslam, who was stopped by police after the attacks but let go and allowed to travel on to Belgium.

Belgian Prime Minister Charles Michel, meanwhile, announced Brussels would remain at the highest alert level for at least another week, maintaining security measures that have severely disrupted normal life in the Belgian capital since the weekend.

Michel cited a "serious and imminent" threat," to the city, which houses the headquarters of the European Union and NATO, and said the rest of the country would stay at the second-highest level. Belgium's crisis center said the alert level would only change if a significant breakthrough warranted it.

The increased security measures in the wake of the massacre in Paris have virtually shut down the Belgian capital, with the subway system, many shops and schools remaining shut yesterday. Michel said that despite the continued high-alert level, schools would reopen tomorrow, with parts of the subway system beginning to operate the same day. He did not say when the system would be completely online again.

"We are very alert and call for caution," Michel said. "The potential targets remain the same: shopping centers and shopping streets and public transport."

"We want to return to a normal way of life as quickly as possible," he added.

The unprecedented security measures come as authorities hunt for one or more suspected extremists, including Abdeslam.

Belgian authorities have not announced any details of their investigation into potential attacks nor have they released any information about four suspects who have been arrested and charged with terrorism-related offenses. These include one suspect who was arrested as part of a sweep that saw 21 people detained since Sunday night. Fifteen of those detainees have since been released.

Earlier yesterday, British Prime Minister David Cameron said during a visit to Paris that he would seek parliamentary approval for the U.K. to join the airstrikes being carried out by the U.S., France, Russia and other nations against the Islamic State extremists in Syria.

Cameron and French President Francois Hollande paid a visit to the Bataclan concert hall, which saw the worst of the carnage. Seeking a unified strategy on Syria, Hollande meets Tuesday with President Barack Obama and with German Chancellor Angela Merkel on Wednesday, before traveling to Moscow on Thursday to meet with Russian President Vladimir Putin.

France's Defense Ministry said it had launched its first airstrikes from the Charles de Gaulle aircraft carrier, bombing IS targets in the Iraqi cities of Ramadi and Mosul in a seven-hour operation. The ministry said four Rafale fighter jets were sent from the carrier yesterday afternoon. France has already carried out strikes against IS targets in Syria.

Britain has been carrying out airstrikes in Iraq, and Cameron has long wanted an expanded mandate to extend the air campaign to Syria. But until now, his government has been reluctant to suggest a parliamentary vote until it could be certain of winning it.