There is a heightened risk of terrorist attacks at Christmas because of the 'Christian aspect' of the holiday, a security expert has warned.

Europe is on high alert after a gun attack on a Christmas market in Strasbourg that killed four people. The BBC reports that a fifth person is brain dead and 11 others are wounded.

The suspect in Tuesday's attack, Cherif Chekatt, was shot dead by police on Thursday night.

There were echoes of an attack in Germany in 2016 when a truck was driven into a Christmas market in Berlin, killing 12.

An unnamed senior counter-terror source told the Daily Mirror that public gatherings at Christmas were an 'obvious target' for attacks.

Another security expert, Colonel Richard Kemp, told the newspaper that the Islamic State could be looking for opportunities to attack in Europe after being pushed back in the Middle East.

He added that Christmas is a riskier time of the year being a Christian celebration.

'This time of year is the highest at risk period because of the combination of large crowds of people enjoying themselves, perhaps not paying as much attention to security as they would normally - and the fact that there is the Christian aspect to it,' he said.

'It is an obvious target and recent history has led us to believe we should all be on our guard at this time.

'Everybody should be vigilant against the possibility of an attack and Islamic State would of course like to hit back as a time when they are being hit so hard in the Middle East.'

ISIS has claimed responsibility for the Strasbourg attack and its supporters reportedly celebrated after news of the rampage broke.

Police in Aberdeen, Scotland, have told shopping centre bosses to have '60-second security' plans in place in order to ensure rapid evacuation in the event of a terrorist attack.

According to the Press and Journal newspaper, police said Strasbourg showed that a terrorist attack 'can happen anywhere'.

The Daily Mail reports that Christmas markets across the UK implemented numerous security measures, including large concrete blocks and crash barriers, as well as increased armed police patrols and bag searches.