Thirteen people have died and around 100 have been injured after a van ploughed into a crowd of people in Las Ramblas, in the center of the city.
New Delhi offers sympathy for the victims and their families and condemns violence in all its forms.
Europe Union again in Spain target of suspect ISIS attack, the suspected militant drove a van into crowds in Barcelona, killing 13 people, in what police suspect was one of a planned wave of attacks.
Daesh claimed responsibility for the deadly rampage along the city´s most famous avenue on Thursday, which was packed with tourists taking an afternoon stroll.
The death toll could rise, with more than 100 injured, authorities said.
As security forces hunted for the van´s driver, who was seen escaping on foot, police said they had killed five attackers on Thursday night in Cambrils, a town south of Barcelona, to thwart a separate attack using explosive belts.
Six civilians and a police officer were injured in Cambrils when the attackers ran them over in a car, before police shot them dead and carried out controlled explosions.
Before the van ploughed into the tree-lined walkway of Las Ramblas, one person was killed in an explosion in a house in a separate town southwest of Barcelona, police said.
Residents there were preparing explosives, a police source added.
Police said they had arrested a Moroccan and a man from Spain´s north African enclave of Melilla, though neither was the van driver.
A third man was arrested in the town of Ripoll on Friday in connection with the attack.
It was still not clear how many people had been involved in the van attack and other incidents on Thursday. Witnesses to the van attack said the white vehicle had zigzagged at high speed down Las Ramblas, ramming pedestrians and cyclists, sending some hurtling through the air and leaving bodies strewn in its wake.
The injured and dead came from 24 different countries, the Catalan government said on Friday in a statement, ranging from France and Germany to Pakistan and the Philippines.
Spanish media said several children were killed.
British tourist Keith Welling, who arrived in Barcelona on Wednesday with his wife and 9-year-old daughter, said they saw the van drive past them down the avenue and took refuge in a restaurant when panic broke out and the crowd started running.
“People were shouting and we heard a bang and someone cried that it was a gunshot … Me and my family ran into the restaurant along with around 40 other people.
“At first people were going crazy in there, lots of people crying, including a little girl around three years old.”
It was the deadliest attack in Spain since March 2004, when militants placed bombs on commuter trains in Madrid, killing 191 people and wounding more than 1,800.
Spanish Prime Minister Mariano Rajoy announced three days of official mourning.
The Spanish royal household said on Twitter: “They are murderers, nothing more than criminals who are not going to terrorise us. All of Spain is Barcelona.