By Robert-Jan Bartunek

BRUSSELS (Reuters) - Belgium is deploying hundreds of troops to guard possible terrorism targets, including Jewish sites and diplomatic missions, following deadly raids on an Islamist cell, the defense minister said on Saturday.

Up to 300 military will be stationed at locations such as the U.S. and Israeli embassies in Brussels and NATO and EU institutions.

"It's very important to say that this wasn't a simple decision, but it was necessary, at a time when police are overly engaged, for the army to enter in a supporting role," Defense Minister Steven Vandeput told reporters.

Troops will reinforce police at least until Thursday, when authorities will review the national threat level, set at 3 on a scale of 4 this week.

The government raised the threat level after a raid in the east Belgian town of Verviers on Thursday in which police shot dead two gunmen. Authorities said the Islamist cell had been preparing an attack on police.

The first military company to be deployed on Belgium's streets was the Chasseurs Ardennais, an infantry unit from the Ardennes region.

Among the places the soldiers are protecting in Brussels is the Jewish Museum, which last May was the site of an Islamist attack, when a lone gunman burst into the then unguarded site and killed four people.

There will also be soldiers in Antwerp, the country's second largest city, which has a large Jewish community, the minister said.

"In Antwerp the largest threat is there," Vandeput said, referring to the Jewish community. "It is also where people are most worried."

Troops with machineguns were on guard outside Jewish schools in Antwerp, while in Brussels soldiers were standing outside EU institutions.

The raids in Verviers on Thursday drew attention to the large number of Belgians drawn to fighting in Syria and elsewhere in the Middle East, then returning home radicalized.

(Additional reporting by Yves Herman and Barbara Lewis; editing by Andrew Roche)