Travel advice provided to Americans by the US State Department says that the Schengen agreement on open borders in Europe makes terrorism more likely in Sweden.

The current warning to visitors to the country says: “Like other countries in the Schengen area, Sweden's open borders with its Western European neighbours could permit terrorist groups to enter and exit the country with anonymity."

However, border checks were re-introduced by the Swedish authorities in November 2015 because of the the number of asylum seekers entering the country.

The UK Foreign Office reported at the time: “Border controls have been reintroduced at the Oresund crossing [from Copenhagen to Malmo] and on ferries from Denmark and Germany.”

The US State Department warning for Europe as a whole says: “Terrorist groups continue to plot attacks in Europe as foreign fighters return home from Syria and Iraq, while other individuals may be radicalised or inspired by Isis propaganda.

“European authorities continue to warn of additional attacks on major events, tourist sites, restaurants, commercial centres, places of worship, and the transportation sector, frequently prompting heightened security at notable public venues and coordinated counterterrorism operations.”

In pictures: Stockholm truck attack Show all 15 1 /15 In pictures: Stockholm truck attack In pictures: Stockholm truck attack 3 people dead when a truck crashed into Ahlens department store in central Stockholm, Sweden Rex In pictures: Stockholm truck attack People were killed when a truck crashed into department store Ahlens on Drottninggatan, in central Stockholm Reuters In pictures: Stockholm truck attack Special Police forces work at the scene where a truck crashed into the Ahlens department store at Drottninggatan in central Stockholm Getty Images In pictures: Stockholm truck attack Woman is assisted at the scene after a truck crashed into an Ahlens department store in Stockholm Rex In pictures: Stockholm truck attack A policewoman in a gas mask operates at the scene where a truck crashed into the Ahlens department store at Drottninggatan in central Stockholm Getty Images In pictures: Stockholm truck attack People react at the scene where a truck crashed into the Ahlens department store at Drottninggatan in central Stockholm Rex In pictures: Stockholm truck attack Reports say three people have died after a truck crashed into an Ahlens department store in Stockholm Rex In pictures: Stockholm truck attack Armed police operates at the scene where a truck crashed into the Ahlens department store at Drottninggatan in central Stockholm Getty Images In pictures: Stockholm truck attack People react at the scene where a truck crashed into the Ahlens department store at Drottninggatan in central Stockholm Getty Images In pictures: Stockholm truck attack Emergency services close to the scene of an incident in Drottninggatan, a street in the centre of Stockholm, Sweden Lasse Gare/PA Wire In pictures: Stockholm truck attack Passers react at the scene where a truck crashed into the Ahlens department store at Drottninggatan in central Stockholm Getty Images In pictures: Stockholm truck attack People killed in incident when a truck was driven into a department store in central Stockholm Reuters In pictures: Stockholm truck attack Police officers work at the scene where a truck crashed into the Ahlens department store at Drottninggatan in central Stockholm Getty Images In pictures: Stockholm truck attack A general view shows a Ahlens department store after a truck reportedly crashed into it, at Drottninggatan in central Stockholm, Sweden EPA In pictures: Stockholm truck attack A view of a street after a truck reportedly crashed into a department store in central Stockholm, Sweden EPA

Immediately after the Stockholm truck attack, the American Embassy in the city warned: “US citizens should avoid this area at this time, heed guidance from local authorities, and maintain security awareness. Please monitor media and local information sources and factor updated information into personal travel plans and activities.

“We strongly encourage US citizens in Sweden to directly contact concerned family members in the United States to advise them of your safety.

The UK Foreign Office warned British travellers: “There are reports that incidents have occurred in Drottninggatan and Fridhemsplan in central Stockholm. You should stay away from public areas if possible and follow the advice of local authorities.”