The European Union parliamentary building complex in Brussels that had been evacuated after a suspicious vehicle was spotted early Monday morning has now been reopened, police authorities in Brussels said.

A bomb threat at four European Parliament buildings and the American embassy led to the immediate evacuation of hundreds of people on Monday morning, the Associated Press reported. One suspect has been arrested.

"Bomb alert here at European Parliament in Brussels," tweeted Irish MEP Luke "Ming" Flanagan. "Currently being evacuated."

Around noon on Monday, about 500 people were evacuated from four European Parliament administrative buildings and a visitors' center in central Brussels after a suspicious-looking man, wearing a military uniform and carrying car keys, had been spotted near the city's parliament, Parliament spokesman Jaume Duch Guillot said.

After being apprehended by authorities, the suspect's car keys were discovered to fit a nearby car, according to Expatica.

Closing down nearby streets to all traffic, Belgian authorities and a bomb disposal unit DOVO investigated the car by using a sniffer dog and a police robot, a spokeswoman for the parliament said, adding that nothing dangerous had been found.

Shortly after 1 p.m., the administrative buildings were reopened and the staff was given the OK to return to their desks, she added. The evacuation was mostly a precaution, a representative for the European Parliament said.

Meanwhile, the American embassy was also evacuated after receiving a bomb scare on Monday morning. However an hour later, the ban was lifted, The Washington Times reported.

Since the terror alert level was raised two weeks ago, Belgian police have had to make dozens of interventions, with police authorities warning that those found guilty of a bomb hoax will face harsh punishment.

In December, three men had been detained after Belgian police stormed an apartment building in the western city of Ghent to end a siege where an alleged hostage was being held, the Associated Press reported.