Student arrested on suspicion of plotting Christmas market terror attack in support of Isis

They said data carriers and "items related to Islam" were seized from the property.

The teenager, who is a student at the Catholic University of Lublin, is alleged to have intended to commit an attack using explosives and planned to join a terrorist organisation, according to Poland's special services spokesman Jacek Dobrzynski.

"The man was very fascinated by Islam, sought to establish contacts with the Islamic State, and was preparing an attack in Poland, in one of the cities during a Christmas market," Mr Dobrzynski told a press conference.

He declined to say in which city the alleged attack was to be carried out so as "not to cause panic".

The prosecutor's office charged Mateusz W. with "undertaking preparatory actions to carry out a terrorist attack that could have resulted in the death or serious injury of many people".

The court ordered him to be detained for three months.

In another case in mid-June, Poland charged three 19-year-old men suspected of gathering pyrotechnic materials and planning terrorist actions, reportedly including an attack on a school in the northern Polish city of Olsztyn.

"You are familiar with this issue from Olsztyn, now we have another example of preparing an attack before Christmas," Mr Dobrzynski added.

"We are shocked by the incident in Sydney, we are shocked by the attacks that occurred in previous years before Christmas in other European countries. Let's remain vigilant."

Christmas markets in Europe have been targeted in multiple attacks in recent years.

This includes a car ramming attack at a market in the German city of Magdeburg last December, which left six people dead.

Authorities said at the time the suspect used emergency exit points to drive onto the grounds of the market, where he allegedly picked up speed and ploughed into the crowds, hitting more than 200 people in a three-minute attack.

Germany has stepped up security measures at some of its Christmas markets, including in Berlin and the city of Augsburg.

Large concrete barriers, checkpoints at entrances, video surveillance and trained security staff are among the security additions made at Berlin's Gendarmenmarkt market.

David Russ, head of production at the event, said: "The requirements have become increasingly stringent."

He added that the added measures "give guests a feeling where they can say 'OK, I can just let go of everything here - I feel safe'".