German police announced Saturday evening they were searching the cathedral in the western city of Cologne with sniffer dogs following a "danger warning" for New Year's Eve. Meanwhile three people were detained in Austria for suspected involvement in an "Islamist network".
"Even though the information relates to New Year's Eve, we are from this evening doing everything we can to ensure the safety of visitors of the cathedral on Christmas Eve," Cologne police chief Michael Esser said in a statement.
After the evening mass and "in agreement with the head of security at the cathedral", the site was searched with sniffer dogs and closed, police said.
Visitors on Sunday were subjected to security checks before entering the Cologne Cathedral.
The German daily Bild reported on its website that officials in Austria, Germany and Spain have all received indications that an Islamist group was planning several attacks in Europe, possibly on New Year's Eve and Christmas.
According to the newspaper, the targets of these attacks could be Christmas masses in Cologne, Vienna and Madrid.
Austria detains suspected Islamists amid security fears
Austria on Sunday said three people were detained for suspected involvement in an "Islamist network".
Austrian police have also stepped up checks, especially around churches, religious events and Christmas markets in Vienna, citing an "increased risk".
Austrian authorities "intervening in an Islamist network" made four arrests Saturday, the interior ministry said Sunday.
A ministry spokesman said three of the four had been detained pending further investigations.
"There was no immediate threat of an attack in Vienna," he told AFP, declining to comment further.
According to the German daily Bild, one arrest was also made in Germany.
The arrested suspects are said to be Tajiks who allegedly wanted to carry out attacks for Islamic State-Khorasan (IS-K), an IS offshoot in Afghanistan, Bild reported.
"Terrorist actors across Europe are calling for attacks on Christian events -- especially around December 24th," Vienna police said in a statement.
German Interior Minister Nancy Faeser pledged a firm response to any extremist threat.
"We all love our Christmas traditions and won't allow ourselves to be intimidated or have our way of life hemmed in," she told regional media group Funke.
However "we take the danger of Islamist terror very seriously and are extremely vigilant", she said. "Our security authorities have their sights on the Islamist scene and are acting decisively as the current measures show."
Besides Austria and Germany, Spain also received indications that an Islamist group was planning several attacks in Europe, possibly on New Year's Eve and Christmas, Bild said.
In July, a cell of suspected Islamists from IS-K was dismantled in Germany and the Netherlands.
Those arrested in Germany were said at the time to have been planning an attack in the country.
