One of the four suspects arrested over the attacks which killed 15 people and injured over 100 others told a court Tuesday that the jihadists wanted to carry out a major attack targeting monuments with explosives.

“We already have a police presence at the Sagrada Familia, there are already measures in place,” the interior minister with the regional government of Catalonia, Joaquim Forn, told a news conference.

“What we have to see is how to intensify them in a way that is compatible with the visits” to the spectacular church designed by Catalan architect Antoni Gaudi, he added.

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Giant planters used to prevent traffic access in Madrid's Gran Via. Photo: AFP

“This will certainly be one of the places where police presence will be immediately intensified,” he added after meeting Barcelona mayor Ada Colau and the representative of Spain's central government in Catalonia, Enric Millo.   

Spain kept the terrorist alert unchanged at the second-highest level after police broke up the group suspected of carrying out the vehicle attacks claimed by the Islamic state group in Barcelona and the nearby seaside resort of Cambrils last week.

“This nevertheless allows us to increase our (security) resources,” Forn said.

Catalan police will boost their presence on the streets by 10-20 percent, he said.   

Police will also ramp up numbers at airports and train stations, “major tourist locations”, and events that draw huge crowds such as football matches, concerts or demonstrations.

A technical commission will study the need to set up security barriers at the seaside city's main thoroughfares that could block the entry of vehicles, Colau said.

Colau has come under fire for the absence of bollards — short concrete posts designed to stop vehicles from driving onto sidewalks like Las Ramblas in Barcelona where a van mowed down pedestrians last Thursday, killing 13 and injuring over a hundred.