BRUSSELS — Heavily armed police and soldiers patrolled key intersections and subways were closed 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 that 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.

And in Turkey, officials detained 26-year-old Ahmad Dahmani, a Belgian national of Moroccan origin, who was believed to have been in contact with the Paris attackers.

Authorities across Europe, 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.

Belgium’s national Crisis Center had 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 were patrolling 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 recommended 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.

The prime minister, speaking at a news conference after the emergency government meeting, said, “We urge the public not to give in to panic, to stay calm. We have taken the measures that are necessary.”