Police arrested 13 people during a series of raids across Belgium, five of whom were later charged with "participating in the activities of a terrorist group", federal prosecutors' spokesman Eric Van der Sijpt told AFP.
He earlier told a news conference that the group, some of whom had recently returned from Syria, was "on the verge of carrying out terrorist attacks to kill police officers on public roads and in police stations."
Police found four Kalashnikov rifles, explosives, ammunition and communications equipment during the raids, along with police uniforms.
Jihadist Twitter accounts later identified the two dead men as Radwan Haqawi and Tareq Jadoun and published what it said was a photo of them in Syria. Belgian authorities did not confirm their identities.
Two other Belgians were arrested in France after allegedly fleeing the raids and were headed towards Italy, police sources said. Belgium has asked for their extradition.
Belgian prosecutors said there were no immediate links with last week's Islamist attacks in Paris on the Charlie Hebdo satirical magazine, a Jewish supermarket and a policewoman, in which 17 people died.
French police separately arrested 12 people overnight and questioned them about "possible logistic support" they may have given to the Paris gunmen -- Islamist brothers Said and Cherif Kouachi and Amedy Coulibaly, sources said.
In Germany an alleged leader of a Turkish and Russian group planning to carry out an attack in Syria and the man in charge of financing were arrested in raids on suspected Islamist sites in and around Berlin by more than 200 police officers, officials said.
- Violent protests -
Thousands demonstrated across the world and violent clashes erupted in Niger and Pakistan as Muslims vented fury over a new Prophet Mohammed cartoon published by Charlie Hebdo.
Four people were killed and 45 injured in protests in Niger's second city of Zinder that turned violent with demonstrators ransacking three churches and torching the French cultural centre.
At least three people were injured when protesters clashed with police outside the French consulate in Karachi, Pakistan. Among them was an AFP photographer, who was shot in the back.
The United States condemned the violence, saying there was a "universal" right of the press to freely publish any kind of information, including caricatures.
- Joining forces -
In Washington, US President Barack Obama and British Prime Minister David Cameron vowed to help France and others defeat global terrorism with stronger cooperation and surveillance.
"We will continue to do everything in our power to help France seek the justice that is needed... to defeat these terrorist networks," Obama said.
However, Obama added that integration of Muslim communities could be better in Europe and said "it's important for Europe not to simply respond with a hammer and law enforcement and military approaches to these problems."
Belgian Prime Minister Charles Michel said he was ready to call up the army to ensure security in the wake of the raids. He raised the country's terror alert to three on a scale of four.
Jewish schools in Brussels and the port city of Antwerp closed Friday. The raid comes less than a year after four people were shot dead in an attack on the Jewish Museum in Brussels. A Frenchman who fought in Syria has been charged with the murders.
With France still reeling from the attacks which targeted its cherished traditions of free speech, US Secretary of State John Kerry laid wreaths on Friday at both the Charlie Hebdo offices and the Jewish supermarket during a visit to Paris.
French President Francois Hollande meanwhile urged the world to offer a "firm" and "collective" response to the attacks, which prompted millions of people to take to the streets in France to show solidarity with the victims.
Charlie Hebdo, which inflamed Muslims in many countries by printing cartoons of the Prophet Mohammed, also laid to rest its slain editor-in-chief Stephane Charbonnier, alias cartoonist Charb, on Friday.