An Uzbek man confessed Tuesday to ramming a stolen truck into a crowd in Stockholm, killing four people and wounding 15, his lawyer said.

The Stockholm District Court ruled that police could detain Rakhmat Akilov for a month after he admitted in court that he drove the stolen beer truck into a crowd outside an upscale department store in central Stockholm on Friday afternoon. He was detained by police hours later and arrested early Saturday.

Police have not given a motive for the attack and no extremist group has claimed responsibility. Police said Mr. Akilov was known to have been sympathetic to extremist organizations but that there was nothing to indicate he might plan an attack. His Swedish residency application was rejected last year.

After the court hearing, Akilov's lawyer, Johan Eriksson, said Akilov is "pleading guilty" to Friday's attack but said he was not allowed to say more about the case.

The four people killed were two Swedes, a Belgian woman, and a British man. The British government has identified the Briton as Chris Bevington, an executive at Swedish music-streaming service Spotify. The others have not been publicly identified.

Eight of those injured, two seriously, were still being treated in the hospital.

Sweden observed a minute of silence Monday on a national day of mourning for the victims, with Swedish royalty, foreign diplomats and politicians among the crowds gathering for a noon observance outside Stockholm City Hall, where Prime Minister Stefan Lofven said "the whole of Sweden" sympathized with the families and friends of the victims.

The victims' home countries suffered "horrendous acts of terrorism, but we have also seen the strength and determination and power of our democratic societies," Mr. Lofven said.

"We will never surrender to terror. We will get through this together," he said.

Swedes have poured into downtown Stockholm since the attack, building a wall of flowers and scribbling notes on sidewalks and wooden boards in memory of the victims, and encouraging people to refrain from despair or hate.

Earlier Monday, some gathered outside the Ahlens department store, among them John Holmstrom, an employee who said he'd been at work just two hours before the attack.

"It's been a real shock, all this week and everything around this weekend about this accident," Mr. Holmstrom said. "I know a lot of people that were really, really close to getting hit by the truck."

The United Nations Security Council condemned "the barbaric and cowardly terrorist attack" in the strongest terms on Monday and reiterated that "any acts of terrorism are criminal and unjustifiable, regardless of their motivation, wherever, whenever and by whomsoever committed." The council underlined the need to bring the perpetrators to justice.

The White House said in a statement that President Trump called Lofven on Sunday and "the two leaders agreed to maintain and strengthen the already close partnership between the United States and Sweden in the global fight against terrorism."

In February, Mr. Trump surprised Swedes when he suggested Sweden could be the next European country to suffer the kind of extremist attacks that have devastated France, Belgium, and Germany.

In 2015, a record 163,000 asylum-seekers arrived in the country – the highest per capita rate in Europe. The government responded by tightening border controls and curtailing some immigrant rights.

Officials have acknowledged the difficulty of keeping tabs on asylum-seekers who have been ordered to leave the country after their applications were turned down.

Police said the truck attack suspect was known for having been sympathetic to extremist organizations. But Swedish police chief Dan Eliasson said "there was nothing in the system that indicated that he would do anything like what happened on Friday."

"If we would have had knowledge, information, of course we would have acted differently. But no such information [was] in the system and that's very important to note," he said.

Chief Eliasson conceded there were "a huge number of persons" who have been denied asylum and the right to stay in Sweden, describing it as a problem.

"I think we have the same problem in all European countries," he said. "It is difficult to return people to some countries [which] will not either accept the return of their own citizens or, if we return them by force, they will be subject maybe to punishment in those countries."

The prosecutor's office said Tuesday that it will revoke the arrest of a second man police had detained Sunday because they suspected he was involved in the case.

According to the prosecutor, "the suspicions have weakened" against him, and there were no grounds to apply for a detention order.

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The statement said he would not be set free but instead "be taken into custody due to a previous decision that he shall be expelled from Sweden."

Associated Press Writer Edith M. Lederer contributed from the United Nations in New York.