"This issue, from the point of view of national security, should be considered very serious. It is of the greatest gravity. This is the fourth incident in the last few months, it’s not normal,” said a member of parliament for the CDS-PP centre-right party Telmo Correia, speaking to journalists in parliament.

Two Algerian men absconded from Lisbon airport on Thursday afternoon when a group of five Algerians (four men and a woman) were boarding a plane bound for Algiers, and “managed to climb over the protection fence around Lisbon airport,” said the PSP spokesman. The two men were detained at a nearby train and bus station early on Friday.

Three other similar incidents have occurred at the airport in the Portuguese capital since July 2016.

The party has called for the Minister of Internal Administration, Constança Urbano de Sousa, to be called to parliament about the issue and plans to “return to the conversation where we left off,” when the minister said that “security has been increased and the problem has been solved.”

“Is it a problem with security? Is it a network, an organisation that is causing these situations? Correia asked.

In October 2016, the Foreigners and Borders Service (SEF) and the PSP prevented three passengers newly arrived at Lisbon airport from Morocco from escaping.

In September an Algerian citizen, travelling between Algeria and Casablanca illegally left Lisbon airport.

At the end of July four men were detained by the PSP at Lisbon airport for violating security rules when they tried to avoid passport control by running across the airport runway.