“These arrests demonstrate once again that ISIS remains a serious threat to the West,” Counter Extremism Project chief executive Ambassador Mark Wallace said. “ISIS is not only trying to take advantage of Hamas’s war against Israel to motivate its supporters and sympathisers but is also attempting to organise terror attacks in Europe to demonstrate its continued relevance within the terrorist milieu. “Authorities must continue to increase their co-operation to ensure the futility of these efforts.” Austria on Sunday said three people were detained for suspected involvement in an “Islamist network”. However, the interior minister said there was “no immediate threat” of an attack in Vienna. “Terrorist actors across Europe are calling for attacks on Christian events,” Vienna police said. One person has been arrested in Germany and the country's Interior Minister Nancy Faeser has 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 said. “Our security authorities have their sights on the Islamist scene and are acting decisively as the current measures show.””