The cell behind the deadly attacks in Spain that left at least 14 dead has been "completely dismantled", according to Interior Minister Juan Ignacio Zoido, as police continued a manhunt for one remaining suspect.

The cell is believed to have consisted of at least 12 young men, many of them Moroccan.

Spain will maintain its security alert at four, one notch below the maximum level, which would signal an attack was imminent, Zoido said on Saturday.

"We are going to redirect our efforts and will adapt these to every place or area that needs special protection," Zoido told a news conference.

He said that the government would reinforce security in crowded areas and tourist hotspots.

The Islamic State of Iraq and the Levant (ISIL, known as ISIS) group has claimed the attacks, which occurred on Thursday and Friday in the northeastern region of Catalonia.

Authorities said the attacks in Barcelona and the seaside resort of Cambrils were related and the work of a large cell that had been plotting for a long time from Alcanar, 200km from Barcelona.

Three Moroccans and one Spaniard are in police custody.

Spanish police on Saturday expanded a manhunt for one of the main suspects, 22-year-old Younes Abouyaaquoub.

READ MORE: Barcelona and Cambrils attacks - What, where and when?

Early in the day, police searched two buses in northwest Catalonia in the hunt for any remaining members of the cell. Nothing was found in the searches in Girona and Garrigas, police said on Twitter.

Across the Pyrenees, French police carried out extra border checks on people coming from Spain.

Officials also announced a series of controlled explosions on Saturday in Alcanar, where the attacks were planned from a rented house, which was destroyed in a blast on Wednesday.

Authorities had initially written off the incident as a household gas accident.

They now believe the explosion, which killed at least one person and injured one of the people currently in custody, actually prevented a far deadlier attack, possibly a vehicle bomb.

The blast forced the suspects to use more "rudimentary" vehicles instead, police said.

In a tweet on Saturday, Catalan police urged Alcanar residents not to be alarmed by the controlled explosions.

Police in Catalonia said three of the suspects shot dead in Cambrils were Moroccan nationals, identifying them as Moussa Oukabir, 17, Said Aallaa, 18, and Mohamed Hychami, 24.

Moussa's brother Driss was one of the four arrested.

In Morocco, their father Said said he was "in shock" and "completely devastated" by the news.

Moussa had been studying "normally" at school while Driss worked "honestly", he told the AFP news agency.

"I hope they will say he's innocent [...]. I don't want to lose my two sons."

The dead and wounded in the two attacks came from 34 countries.

The Catalan interior ministry said 59 people were still in hospital, including 15 in critical condition.