"I recommend to Portuguese who travel - for tourism or for work - to use the ‘Registo Viajante’ application," José Luís Carneiro told Lusa. "It's a free mobile app that enables us to have a database of the Portuguese who are in movement. They're Portuguese who don't usually register at consulates [as Portuguese citizens living abroad may do], because they're in the countries on a very temporary basis."

Carneiro stressed that the personal data registered by the app are protected.

The app makes it possible in circumstances such as Thursday's attacks in Barcelona and Cambrils to check "whether or not there are Portuguese” among the victims, and also makes it possible for users to send requests for help - smoothing contacts between the authorities in Portugal and the country where the travellers are.

So far no Portuguese nationals have been identified as being among the dead and injured, Carneiro said, adding that the situation was still being monitored.

He also recommended that Portuguese travelling abroad should avoid places with large concentrations of people, given the fears of the authorities that there may be copy-cat attacks in the wake of the incidents in Catalonia.

The attack in Barcelona, around 5pm local time on Thursday, killed 13 and left around 100 injured, after a van drove into people on the Ramblas, in the centre of the city. The Islamic State group claimed responsibility.

Catalan police have already detained three men suspected of being involved in the attack, and another suspect was found dead 12 kilometres from Barcelona after an exchange of gunfire with police when he tried to force his way through a police checkpoint.

A separate attack in the centre of Cambrils, a resort 117 kilometres south-east of Barcelona, where another vehicle drove into several people, ended with police shooting five "suspected terrorists" dead.