Terror fears are growing across Europe as British synagogues have been put on high alert following explosions in Denmark on Wednesday.

The explosions are being investigated outside the Israeli embassy in Copenhagen and follow Israel‘s ground invasion of Lebanon, sparking fears of an all-out war in the Middle East after Iran joined the fray directly attacking Israel with nearly 200 ballistic missiles. 

In Europe, Danish police said they had detained three young Swedish men, aged between 15 and 20, for questioning them following the explosions, which they said were likely caused by hand grenades.

Two men thought to be involved in the attack were apprehended while on a train in Copenhagen’s main train station, while the third was found elsewhere in the city.

Copenhagen Police Chief Superintendent Jens Jespersen said the detonation of the devices caused damage to a building around 100 metres from the embassy.

He told reporters: “We can’t say for sure if the embassy has been or not been the target of these explosions We are also investigating if they have acted alone, on request or together with others.”

Jepsen did not reveal any further information about the three young men’s connection to the incident, but preliminary charges are expected to filed against two of them for illegal weapons possession.

A spokesperson for the embassy said: “We are shocked by what has happened. No one was injured, and no one was present at the embassy when the explosions occurred.”

This came as UK charity the Community Security Trust (CST) issued a warning over the rising number of attacks on Jewish organisations and buildings coinciding with the rising tensions in the Middle East.

It released a security notice to British synagogues urging strict security provisions. It read: “Hezbollah and Iran have a long record of terrorist attacks against Diaspora Jewish communities.”

The charity called for synagogues to be on high alert for “suspicious people and activities”, adding that people should know “how to lock down and barricade” in case of emergencies.

Mark Gardner, Chief Executive of CST, said: “We will be working in partnership with police up and down the country to keep synagogues and communal areas safe, which is our number one priority. Remember if you see anything suspicious, report it to police and CST immediately.”

Laurence Julius, the vice-chairman of the Advisory Board of the National Jewish Assembly, added to this concern. He told the Sun Online: “Like all synagogues in the UK, our synagogue is in regular contact with the CST and local police.

“In view of the current situation, additional measures will be in place to protect the security of our community within the synagogue and on entering and leaving.