As Spain mourns, security has been heightened as police continue their search for clues after two deadly attacks.

At least 14 people have been killed in the two attacks to hit Spain this week.

On Thursday, a speeding van ploughed through pedestrians on the famous Rambla boulevard in Barcelona, killing at least 13 people and injuring more than 100 others.

On Friday, a woman died from her injuries following a similar attack in the nearby seaside resort of Cambrils. Five men, who have been described as the perpetrators, were shot dead by police.

And earlier in the week, one person was killed in an explosion that also destroyed a house in the town of Alcanar, 200km south of Barcelona, where bomb makers are thought to have lived.

TIMELINE: Deadly attacks in Europe

Authorities said the attacks in Barcelona and Cambrils were related and the work of a large cell that had been plotting for a long time from Alcanar.

Four arrests have been made, while seven other members of the suspected cell have been confirmed dead.

The incidents in Spain are the latest in a string of attacks across Europe.

Most have been claimed by the Islamic State of Iraq and the Levant (ISIL, also known as ISIS), which is being driven from strongholds in Iraq and Syria.

So how potent are ISIL fighters in Europe?

Presenter: Hashem Ahelbarra

Guests:

Yasser Louati - Human rights activist

Milo Comeford - Tony Blair Institute for Global Change

Greg Barton - Professor of Global Islamic Politics, Deakin University

Source: Al Jazeera