"It is obviously the duty of the [security] services to analyse and assess each piece of information that comes up," e told journalists during a visit to an agricultural trade fair in Póvoa de Varzim, near Porto.

According to Costa, on Wednesday the secretary-general of Portugal's internal security system held “a meeting with top directors of all the security services in the ambit of anti-terror coordination” at which an “assessment was made" that concluded that the current 'moderate' level of alert should remain “in the whole country and in the city of Lisbon, too".

A statement from the office of the secretary-general in question, Helena Fazenda, had earlier stated that the terror threat level "remains at moderate". It also said that "all security forces and services that form part of the Unit of Antiterrorism Coordination are working in close conjunction with their counterparts [abroad], monitoring the international context in the ambit of the terrorist threat."

Contacted by Lusa on why the statement had been issued, Fazenda explained that it was because "rumours" were circulating that the authorities had raised or were about to raise the alert level.

Separately, a spokesman for the national directorate of the PSP urban police force, Hugo Palma, told Lusa that preventative measures had been adopted for some events with large audiences this coming weekend, such as music festivals, but that "there is no identification of any terrorist risk or threat" in Portugal.

According to Palma, police chiefs had simply decided to "reinforce, at the national level, attention to preventative measures in this matter", given the many summer events taking place.

Measures taken include the expansion of the area covered by security perimeters around events, and the putting in place of specific barriers, he said, In addition, policing at the events is to be more visible, even as plain-clothes teams will be patrolling.