The US state department has warned its citizens of the increased risk of terrorist attacks in Europe over the holiday period.

While European authorities are said to have stepped up security at Christmas markets and other outdoor events due to fears they may become a terror target, the travel advisory by the US state department said it remained concerned about the potential for further strikes.

The alert noted attacks had been carried out in Belgium France, Germany and Turkey in the past year.

Gunda Kniep, the manager of one Christmas market in Berlin said: “I think it’s impossible to do more than what we’re doing. Risk can never be ruled out but my hope is that our square in Berlin will not be the focus. At least that’s my hope.”

On Monday, French authorities disclosed they had arrested seven suspects in the cities of Strasbourg and Marseille, saying they had foiled a long-standing terror plot.