The death toll from the deadly twin terrorist attacks in Barcelona has risen to 16.

A German woman who was seriously injured in the van attack on Las Ramblas on August 17 died in the intensive care unit on Sunday, according to the regional health department.

The death of the 51-year-old means the attacks in Barcelona and Cambrils have claimed the lives of 16 civilians.

Fourteen people died in the Las Ramblas attack. Another man was stabbed to death in a carjacking as the van driver made his getaway. A 61-year-old woman was critically injured and later died in hospital in the second attack in Cambrils.

Five people remain in a critical condition.

About 500,000 people marched along the streets in a defiant act of solidarity and peace on Saturday (local time).

Sydney boy Julian Cadman, seven, was confirmed to be among the dead last week. His mother and three other Australians were injured.

After the Barcelona van attack, suspects drove an Audi A3 down a promenade in the coastal town of Cambrils, west of Barcelona. The men crashed the car and attacked passers-by with knives and axes, police said.

Police believe an earlier explosion at a house in Alcanar, 200 kilometres from Barcelona, was also linked to the attacks.

It’s believed the men had planned more sophisticated assaults but were rushed into a hurried attack when the botched homemade bomb accidentally detonated.

Mohamed Houli Chemlal, an alleged member of the Islamist terror, last week told Spain’s High Court that the group planned to attack Antoni Gaudi’s landmark Sagrada Familia church and other Barcelona monuments, a judicial source reportedly told El Mundo.

Four members of the alleged terror cell have been arrested, while the remaining members are believed to have died over the course of the attacks.