Brussels Terror Alert Level Lowered Ahead of Schedule

— -- The terror alert level in Brussels has been lowered to the second-highest level ahead of when the move was expected to be made, officials say.

The city was slated to stay at a level 4 alert, their highest level, until Monday but officials lowered it to a level 3 this afternoon.

Officials said that the step down was approved by the crisis center in charge of analyzing the threat level and means that "the threat is still possible and likely." By bringing it down to a 3, that sets Brussels in line with the rest of the country.

"The reason of this decision was based on the fact that that threat is still serious but no longer as imminent as before," Belgian prime minister Charles Michel said today.

Michel also said that the city's whole subway system will reopen tomorrow, as only 35 of their 69 stops are open today.

This comes hours after envelopes containing unknown powder at a mosque in Brussels today prompted an evacuation of the building. The scare came amid anti-terror raids around the country and a heightened state of alert there.

The spokesman for Brussels firefighters tells ABC News they received an alert at 1:30 p.m. local time. A lab team was sent immediately to the Grand Mosque as well as a bomb disposal team as a precautionary measure.

The spokesman for Brussels firefighters confirms to ABC News that about 10 envelopes were found in one package by the clerk at the Mosque's mail room. All told, 17 people came into contact with the package and were decontaminated as a precaution.

The tests on the powder have come back negative and the substance was believed to be flour or talc, the spokesman told ABC News.