Churches and Christmas markets across Europe have had security tightened amid fears they could be targets for terrorists.
Worshippers at Germany's Cologne Cathedral face searches on Christmas Eve after a security alert prompted police to scour the building with sniffer dogs.
Police were told of a potential threat on New Year's Eve and announced the church would be under “special protection measures”.
They did not confirm the nature of the threat to the cathedral, one of Germany's best-known tourist attractions, with reports suggesting it involved a link to ISIS militants active in Afghanistan.
In Austria, police warned of a heightened threat because of “terrorist actors across Europe calling for attacks on Christian events”, especially on Christmas Eve.
Security measures in Vienna will focus on churches, religious services and Christmas markets and could involve people being searched upon entry, police said.
France meanwhile reported five arrests linked to a suspected threat to a Christmas market in Strasbourg, the site of an attack in 2018 in which five people were killed.
Interior Minister Gerald Darmanin wrote to police chiefs on Friday urging “extreme vigilance” over Christmas because of “persistent tensions at an international level, especially in the context of the Israeli-Palestinian conflict”.
He said the added security measures could remain into the New Year.
Fears of violence have been raised across Europe since the outbreak of the Israel-Gaza war.
Last week, Dutch security services raised the terror threat level in the Netherlands, warning groups such as ISIS and Al Qaeda were using the Middle East conflict to encourage attacks in the West.
Germany has also reported Islamist calls to violence during the Israel-Gaza war. A German tourist was stabbed to death in Paris this month by a man claiming allegiance to ISIS.
Sweden has been on high alert since a spate of Quran-burnings raised tensions over the summer.
The Czech Republic held a day of mourning on Saturday after a mass shooting at a Prague university left 14 people dead and an Emirati couple injured, although authorities do not believe the gunman was motivated by an extremist ideology.
