The explosion, ​which happened around 4 am, blew out the ⁠windows of the synagogue, as well as those of ​a building on the opposite side of the road, public ​broadcaster RTBF said.

The cause was not clear, but prosecutors said the case had been passed to federal authorities, which normally investigate incidents linked ​to terrorism or organised crime.

Belgian Interior Minister Bernard Quintin ​called the explosion “a despicable antisemitic act that directly targeted the Jewish community ‌of ⁠Belgium”.

He said security measures around similar sites will continue to be reinforced.

Eitan Bergman, Vice-President of the Coordinating Committee of Jewish Organisations in Belgium (CCOJB), said the targeting of the synagogue ​was deeply shocking.

“Liege ​is home ⁠to a very small but vibrant Jewish community where I personally grew up. Today, the ​feelings among our community members are a mixture ​of ⁠sadness, worry and profound shock,” he told Reuters.

Police have cordoned off the largely residential street on the bank of the ⁠river ​Meuse opposite Liege city centre.

Federal prosecutors ​declined to give further details of the incident.