BRUSSELS - Heavily armed police and soldiers patrolled key intersections, subways were closed and many stores shut their doors in Belgium's capital Saturday as the government warned of a threat of Paris-style attacks. At least one suspect from the deadly Paris attacks is at large and was last seen crossing into Belgium.

Prime Minister Charles Michel said the decision to raise the threat alert to the highest level was taken "based on quite precise information about the risk of an attack like the one that happened in Paris . . . where several individuals with arms and explosives launch actions, perhaps even in several places at the same time."

The Belgian Federal Prosecutor's office said Saturday several weapons were discovered during the search of the home of one of three people arrested in connection with the Paris attacks, but said no explosives were found.

Authorities across Europe and the Mideast and in Washington are trying to determine how a network of primarily French and Belgian attackers with links to Islamic extremists in Syria plotted and carried out the deadliest violence in France in decades - and how many may still be on the run.

A new potential link emerged Saturday in Turkey, where authorities said they detained a 26-year-old Belgian suspected of connections to Islamic extremists - and possibly to the Paris attacks. The private Dogan news agency identified him as Ahmet Dahmani and said he is suspected of having explored areas in Paris that were targeted in the attacks.

Belgium's national Crisis Center has raised its terrorism alert for the Brussels region to Level 4, which indicates a "serious and immediate threat." Belgium's special security cabinet held an emergency meeting Saturday morning.

Brussels was the home of Abdelhamid Abaaoud, the suspected organizer of the Nov. 13 Paris attacks, and Belgium has filed charges of "participation in terrorist attacks and participation in the activities of a terrorist organization" against three suspects relating to the Paris attacks.

At least one Paris attacker, Salah Abdeslam, crossed into Belgium the morning after the attacks. A Paris police official and the Paris prosecutor's office said Saturday they had no firm information on Abdeslam's whereabouts, including whether he was in the Brussels area.

Police and soldiers patrolled Saturday morning at key intersections of the Belgian capital, a city of more than 1 million that is home to the headquarters of the European Union, the NATO alliance and offices of many multinational corporations.

Residents were told to avoid gatherings, train stations, airports and commercial districts. Service was halted on the Brussels Metro, as well as on streetcar lines that run underground.

As the first snow flurries of the season fell, many stores and commercial centers in the capital shut their doors on what normally would have been a busy weekend shopping day in the lead-up to the Christmas and New Year's holidays. The Royal Museums of Fine Arts of Belgium closed for the weekend, and a Saturday evening concert by French rocker Johnny Hallyday was rescheduled for March, the Palais 21 venue announced on its website.

"We urge the public not to give in to panic, to stay calm. We have taken the measures that are necessary," the prime minister said.