ISIS terror cells are plotting to blow up churches across Europe, intelligence services have warned.

One of the four suspects arrested over the attacks which killed 15 people and injured more than 100 others told a court yesterday that jihadists wanted to carry out a major attack targeting monuments with explosives.

And an Islamic State propaganda magazine has carried a photo of the world-famous Dresden Frauenkirche in its latest edition - below the headline 'Just Terror Tactics'.

Today concrete blocks were installed close to the famous gothic cathedral in Cologne, Germany, in response to the Spanish terror attacks

Also in Germany, heavy stone blocks have been put up around the cathedral in Cologne as a result of intelligence uncovered in the probe into the Barcelona atrocity.

Patrols are being stepped up at tourist sites in Barcelona, including the iconic Sagrada Familia church and major sports and cultural events in the wake of last week's deadly vehicle attacks in Spain, officials confirmed today.

Today pictures showed the blocks being installed in Cologne, blocking entrances to the cathedral, which has stood in its current form since 1880.

Cologne Police president Uwe Jacob said today that the city is increasing its security in reaction to vehicle attacks in Barcelona and the nearby seaside town of Cambrils.

Target: Police say patrols have been stepped up at the Sagrada Famillia Basilica, where a service was held on Sunday to honour those killed in last week's atrocities

Also feared to be on a jihadist hit list is the Dresden Frauenkirche, which features in ISIS magazine Rumiyah

Also feared to be on a jihadist hit list is the Dresden Frauenkirche, which features in ISIS magazine Rumiyah.

An article next to the feature describes it as 'the popular gathering place of the crusaders, waiting to be burned down'.

It went on to state that churches like the Frauenkirche are 'optimal places of attack' because of their close proximity to nightclubs, restaurants and bars.

The Frauenkirche - Church of Our Lady - was destroyed in the controversial Allied bombing raid in 1945 which gutted Dresden's baroque centre and claimed 25,000 civilian lives.

The blackened hulk of the church rotted through the years of the Cold War when Dresden lay in the Communist east.

Fifteen people were last week killed, and more than 100 injured, in terror attacks by an ISIS cell in Barcelona and Cambrils in Catalonia

After reunification the structure was rebuilt using much of the original masonry which was found in the ruins.

The Queen visited the church in 2004 ahead of its reconsecration. The new gilded orb and cross on top of the dome was forged by Grant Macdonald Silversmiths in Londonusing the original 18th-century techniques as much as possible.

Dresden Police President Horst Kretzschmar confirmed that German intelligence had passed on the Isis report to him, which also contains a DIY guide on how to make firebombs.

'Yes, we know that. There is an abstract danger and we are prepared for it,' he told German newspaper Bild.

Heavily armed 'intervention teams' are ready in the background, he added.

After last week's terrorist attack in Barcelona, a new threat analysis was conducted in Germany by the authorities.

Churches are deemed as vulnerable sites and security is being stepped up around them, including at Cologne Cathedral which draws hundreds of thousands of tourists a year.

Terror expert Prof. Peter Neumann from London's King's College told Bild: 'Perhaps the terrorists are now putting more emphasis on such goals. This is shocking, but it fits into the picture because of the perpetrators goal of religious confrontation. '

Germany has been in high alert since ISIS terrorist Anis Amri hijacked a truck in Berlin on December 19 last year and drove it into a Christmas market.

Barcelona mayor Ada Colau has come under fire for the absence of bollards - short concrete posts designed to stop vehicles from driving onto sidewalks like Las Ramblas.