Time for Swedish people to die "like our brothers and sisters", threatening message said ahead of the bombs.

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The explosions in central Stockholm Saturday were a suicide attack, Sweden's SVT television reported. The only person to die in the attack was the bomber, and a bag filled with nails was found near the body, SVT added. Neither the police nor the intelligence service have confirmed this report.

The Swedish news agency TT meanwhile reported that it had received messages about 10 minutes before the blasts in Arab 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."

It urged "mujahideen," or Islamic fighters, to rise up in Sweden and in Europe, the news agency said, adding that the message referred to the Swedish military presence in Afghanistan as part of the US-led international security force.

TT said a similar message was sent to the Swedish Security Service SÄPO.

Officers said they did not know the precise cause of the blasts or if they were linked. One occurred in a car about 200 metres (650 feet) from the other.

The first blast in the car left two people in need of hospital treatment for minor injuries, said emergency services spokesman Bengt Norberg.

A second alert was received two minutes later and one person was found dead at the scene of this second blast which took place in the street, he added.

"I cannot confirm that the death is linked to the explosion of the car but I cannot deny it either," police spokeswoman Petra Sjolandero said.

She added that the car caught fire "following a series of explosions which could have been from gas canisters."