(CNN) -- The explosions that killed one person and wounded two others in central Stockholm, Sweden, were "an act of terrorism," a Swedish police official said Sunday.
Two explosions occurred within minutes of each other Saturday in the district full of Christmas shoppers, Swedish authorities said. A Swedish news agency and police said they received e-mailed threats 10 minutes before the explosions, but Swedish authorities have not confirmed the three events are connected, Prime Minister Fredrik Reinfeldt said Sunday.
The Swedish Security Service said the incidents appeared to be the work of "a single perpetrator." Reinfeldt called the explosions "completely unacceptable" as he mounted an impassioned defense of Swedish society in the face of what seems to be its first suicide bombing.
"This is not the path we want to go down. It is very serious that this has already happened," he said.
"Sweden is an open society," Reinfeldt added. "It is an open society which has demonstrated a will that people must be able to come from different backgrounds, believe in different gods or not believe in any god at all. Be able to live side by side, together, in our open society."
Posts on websites that frequently feature statements and propaganda videos from Islamic radical groups posted a name and photo of a man identified as the attacker on Sunday. But Swedish police did not confirm the name Sunday evening, saying they were still trying to notify relatives of the dead man.
Regional police chief Carin Gotblad said the bomber had "failed."
"While this was a very serious event, no innocent people were seriously hurt. If that was the intention, then the perpetrator failed," she said, adding that the country would not increase its terror threat level.
Anders Thornberg, head of the security measures division for Swedish security police, told reporters Sunday that based on the agency's criteria for terrorism and a chief prosecutor's assessment, "it is our judgment that this was an act of terrorism." He said authorities are investigating whether the two explosions were related to one another, "but there may well be a connection."
On Sunday night, London's Metropolitan Police executed a search warrant in Bedfordshire, north of London, in connection with the Stockholm probe, a police spokesman said.
The spokesman, who would not give his name, said the warrant was executed under Britain's Terrorism Act 2000 and that "no arrests have been made ... and no hazardous substances have been found."
The writer of the e-mailed threats to the Swedish news agency and police mentions the presence of Swedish troops in Afghanistan and a Swedish cartoonist who depicted the prophet Mohammed, according to TT, a Swedish news wire that received the threats.
The e-mails contained sound files featuring a person speaking in Swedish and Arabic, TT reported.
About 500 Swedish troops are in Afghanistan, according to NATO's International Security Assistance Force.
The sender referred to Swedish silence regarding the Afghanistan troops and the controversial cartoon by Lars Vilks that depicted Mohammed as having the body of a dog.
"Now your children, daughters and sisters will die like our brothers and sisters and children are dying," the e-mail states, according to TT.
"Our actions will speak for themselves," the person said in an audio recording attached to the e-mail. "As long as you don't end your war against Islam and the humiliation against the prophet and with your stupid support to Lars Vilks the pig."
Police said the explosions were in a popular pedestrian shopping area.
"One explosion happened at the intersection of Drottninggatan and Olof Palmes Gata," two busy streets in central Stockholm, said police spokeswoman Petra Sjolander. She said the car exploded multiple times.
"It is likely that this was some kind of gas tubes that have caused the car to explode multiple times," Sjolander said.
Two people at the site of the car explosion were hospitalized with minor injuries, Sjolander said.
Video on Sweden's TV4 showed flames spewing from the car, which was parked behind several other vehicles.
A second explosion occurred about five minutes later, at the intersection of Drottninggatan and Bryggargatan streets, Sjolander said.
"We don't know at this point what caused the second explosion," Sjolander said, describing it as suspicious. An unidentified man was found dead at the scene of the second blast. A bag was found near the body, Sjolander said.
"We had bomb technicians on site, but I can't give you any details of what they did," she said.
A bomb robot rolled up to the body and removed the bag for examination, according to the Swedish newspaper Dagens Nyheter.
Thornberg said Sunday that he could not confirm whether the man blew himself up.
When asked about the possibility of suicide bombing in Stockholm becoming a new trend, Thornberg replied, "Yes, absolutely -- if that is the case, then it is very serious."
Thornberg said authorities are working on both intelligence and a normal police investigation and will try to determine "if there may be any more acts of terrorism like this one being planned. At this point, we don't think there are more acts coming, but we can't say for sure."
"What has happened does not signify a change of the current terrorism threat level in Sweden, but we will continuously be reassessing this to see if what has happened warrants a change in threat level," he said.
In a message posted on Twitter Saturday, Swedish Foreign Minister Carl Bildt said, "Most worrying attempt at terrorist attack in crowded part of central Stockholm. Failed -- but could have been truly catastrophic."
Swedish terrorism expert Magnus Ranstorp told CNN that he did not believe the attacker acted alone.
"This was not something where he just woke up and thought that he would blow himself up," said Ranstorp, a professor at the Swedish military academy and a former professor in terrorism studies at the University of St. Andrews in Scotland.
The e-mail writer ended the message with a call for action "to all Mujahadeen in Europe and Sweden," TT said.
"Now is the time to strike, don't wait any longer," the message read, according to TT. "Step up with whatever you have, even if it is a knife, and I know you have more than a knife. Fear no one, fear not prison, fear not death."
TT said that it was not clear from the e-mail or the audio files if the person belongs to any specific organization.
The person claimed to have been to the Middle East and asked family for forgiveness for lying to them. "I didn't go to the middle east to work," the writer said. "I went there for jihad."
CNN's Mila Sanina contributed to this report.