STOCKHOLM — Twin blasts that rocked central Stockholm killing one man were a "terrorist" attack, Sweden's domestic intelligence agency Saepo said on Sunday.
"We are opening an investigation into a terrorist crime under Swedish laws," Anders Thornberg, head of Saepo's security unit, said a day after Christmas shoppers were targeted in the Swedish capital.
The suspected bomber, whose identity has not been made public, was killed but Thornberg told a press conference that it was unclear if he had intended to blow himself up.
"If this was a suicide attack, it would be new in Sweden," he said.
Two people were injured when a car exploded on 5:00 pm Saturday in the busy shopping street of Drottninggatan. A second blast occurred shortly afterwards a few hundred yards away.
Prime Minister Fredrik Reinfeldt's spokeswoman said the government would make no immediate comment on the attack. Stockholm police said patrols would be stepped up.
"Saepo has taken over the investigation," said Stockholm police chief Erik Widstrand at a joint press conference with Thornberg.
Swedish news agency TT said earlier it had received an email about 10 minutes before the first blast in Arabic and Swedish, warning of unspecified "action".
"Our acts will speak for themselves," TT quoted the message as saying. "Now your children, your daughters and your sisters will die as our brothers, our sisters and our children are dying."
Sweden has around 500 troops in Afghanistan as part of the US-led international security force. Their mandate only runs to January 1, and would need to be renewed by parliament for them to stay on.
Punitive actions would continue "as long as you do not stop your war against Islam, your degradation of the Prophet and your stupid support for the pig Vilks," said the statement.
Swedish cartoonist Lar Vilks has been the object of death threats and at least one plot to kill him over a drawing depicting the Prophet Mohammed as a dog.
TT said a similar message had been sent to Saepo.
Saepo's Thornberg said however he had "not read the email in detail but I know that he was not happy to be in Sweden".
"We have armed forces in other countries and bad things have been said about the Prohet etc...," he added, referring to the email.
On October 1, Saepo raised the alert level for attacks from low to elevated, putting it at three on an alert scale of five.
Sheik Hassan Mussa, the imam of Stockholm's grand mosque, deplored "all forms of attacks, violence, fears and threats against innocent people, whatever the motive or pretext", in a statement sent to TT.
The security and stability of Sweden are a religious and social duty, he added.