Brussels will remain under the highest level of alert for another week due to an ongoing “terrorism” threat, but schools and the underground train system could reopen from Wednesday, according to Charles Michel, Belgium’s prime minister.

The army and police will continue to be deployed in force and the country will reduce the number of events with large crowds, for fear of a repeat of the deadly Paris attacks on November 13, Michel said on Monday.

The announcement came as the US state department issued a global alert for Americans planning to travel following the deadly attacks in Paris and Bamako in Mali.

Citing “increased terrorist threats” from armed groups in various regions of the world, the alert did not advise people against travel but warned of potential attackers targeting private or government interests.

“Current information suggests that [Islamic State], al-Qaeda, Boko Haram, and other terrorist groups continue to plan terrorist attacks in multiple regions,” a statement on the state department’s website read.

“Authorities believe the likelihood of terror attacks will continue as members of [Islamic State] return from Syria and Iraq.

“Additionally, there is a continuing threat from unaffiliated persons planning attacks inspired by major terrorist organizations but conducted on an individual basis.”

For his part, Michel said, his government was trying to bring the country “back to normal as quickly as possible” while working with the security services.

“We want progressively to return to normality,” he said.

“Schools in Brussels will open on Wednesday and the metro on Wednesday, too. For the metro it could be done in stages.”

In France, police said that an explosive vest – without a detonator – was found on Monday afternoon by a street cleaner in a pile of rubble in Chatillon-Montrouge, on the southern edge of Paris.

A police official confirmed that the vest – recovered close to where the fugitive suspect Salah Abdeslam’s mobile phone had been found – contained bolts and the same type of explosives as those used in the attacks.

Authorities are continuing to hunt for Abdeslam, a Belgian national, after arresting 21 people in late-night counterterrorism raids since Sunday.

Brussels has been locked down since Saturday with armed police and troops patrolling quiet streets.

Prosecutors in Belgium said they had charged a fourth person with “terrorist” offences linked to the shootings and suicide bombings that killed 130 people in the French capital on November 13. Al Jazeera