Attacks have been rampant in the past few weeks, causing some countries to be wary about security and potential terrorists in the midst. However, while the United States has been debating about whether or not they should still be accepting refugees from Syria, European countries are on high security alert as well.

According to The New Yorker, Belgium's Prime Minister Charles Michel has already reported "several individuals with arms and explosive" possibly attacking the captital on Saturday, marking the first day of the country's lockdown.

Schools and universities have been closed, and soldiers have been patrolling the streets, while entrances to the city's metro system have been compromised, with trains running only above-ground, sometimes late, sometimes not at all.

On Sunday night, a series of raids were held across the country, and for reasons of operational security, the Belgian Federal Police asked locals not to share information about their movements on social media. To perhaps lighten up the mood, Twitter users began posting photographs of cats instead, hashtagged #BrusselsLockdown.

After arrests were made, the federal police responded with a picture of cat food, captioned, "For the cats who helped us last night... Help yourself!"

However, The Atlantic reported that no guns or explosives were found in the raids, and Brussels native Salah Abdeslam, the 26-year-old woman known to be the only survivor from the terrorist attack in Paris on November 13, was not among those detained. She was last seen crossing Belgium just hours after the attack.

French police on Monday said that an explosive belt without a detonator was found in a pile of rubble in Southern Paris, which the Associated Press said is the same location as Abdeslam's cellphone, used on the day of the attacks.

Michel said at a press conference on Sunday, "We fear an attack similar to the one in Paris. A number of individuals could launch an attack on several locations in Brussels simultaneously."

Despite schools and universities still closed on Monday -- already the third day of the lockdown -- European Union buildings have now been opened, although still heavily guarded by the military.

The Belgian Crisis Center announced that Brussels will remain at a level four threat for another week. However, the city is not expected to stay in lockdown for long, as a Euro News reported that the tennis competition -- the Davis Cup final between Britain and Belgium -- is still expected to go on as planned in Gent, 55 kilometers northeast of Brussels, on Friday.