Police in Austria have intensified security measures around the three Taylor Swift concerts taking place in Vienna on Thursday, Friday and Saturday this week.

The move follows the arrests on Wednesday of two people suspected of planning Islamist attacks on large events in the area around Vienna, including the concerts by the US superstar.

The General Director for Public Security, Franz Ruf, said a 19-year-old Austrian citizen was arrested on Wednesday morning in Ternitz in the province of Lower Austria.

He said a second arrest took place in Vienna in the afternoon, but gave no further details about the suspect.

“According to the current status of the investigation, the two suspects became radicalised via the internet,” Mr Ruf said. He said the 19-year-old made “an oath of allegiance” to Islamic State at the beginning of July.

A large police operation took place in Ternitz, where the 19-year-old lived. A number of houses nearby were evacuated while his home was searched.

Mr Ruf said chemical substances had been found and were being examined.

He said the police were taking all measure to ensure that all events around Vienna could take place safely, including the three Taylor Swift concerts.

He added that there would be a special focus on entrance checks to her concerts, which are taking place at the Ernst-Happel Stadium.

Police said the “terror alert level” in Austria remained high and was being continuously evaluated.

The head of police in Vienna, Gerhard Pürstl, said the concrete danger had been ‘minimised”, but that an “abstract danger” remained.

He said 65,000 people a day were expected to attend the concerts, as well as 22,000 fans outside the venue.

Mr Pürstl said that as well as stepping up security checks in and around the concerts, special forces would be deployed in the area around the stadium, as well as police dog teams and anti-terror units.

“Mobile and stationary video surveillance will be carried out. The airspace will also be monitored,” he said, adding that “extensive search measures” would be carried out, including personal searches.

He warned that fans going to see the Taylor Swift concerts could expect delays when they entered the arena, and he urged people to arrive early.

Investigations are continuing.