Belgian police killed two men during one of about a dozen raids Thursday against an Islamist group who was reportedly about to launch large terrorist attacks.

Prosecutors' Spokesman Eric Van der Sypt said that Belgian counter-terrorism attacks have been under way before the attack on French satirical magazine Charlie Hebdo and others last week when Islamist gunmen killed 17 people in Paris,  Reuters reported.  Ever since young Muslims who fought in Syria returned to Europe radicalized, fears of terrorist attacks in the region have been heightened.

Three men opened fire on Belgian police Thursday while trying to get inside of an apartment above a town center bakery in Verviers, Belgium. Two were killed and the third arrested, according to the New York Daily News.

"The suspects immediately and for several minutes opened fire with military weaponry and handguns on specials units of the federal police before they were neutralized," Van der Sypt told reporters at a news conference.

Van der Sypt added that Belgian authorities still expect a number of arrests.

Since the counter-terrorism raids Thursday, Belgium has raised its terror alert to its second highest. Security has been heightened at police stations were terrorists attacks are suspected to occur, according to Reuters.

"The searches were carried out as part of an investigation into an operational cell some of whose members had returned from Syria," Van der Sypt said about Thursday's raids. "For the time being, there is no connection with the attacks in Paris."

On Thursday, another man who is suspected to have supplied Frenchman Amedy Coulibaly with the weapons used to take over a kosher grocery store in Paris last Friday was arrested.

Coulibaly and two terrorist brothers, Cherif and Said Kouachi, were killed after coming together to murder 17 people, including journalists at Charlie Hebdo, over a period of three days of attacks. Coulibaly was responsible for the death of four people at the kosher grocery.

Coulibaly and the two brothers claimed allegiance to Islamist militants in the Middle East.