Twin blasts occurred on Saturday, Dec 11 in a busy street crowded with Christmas shoppers. Police said that a parked car packed with gas canisters exploded at around 4:50 pm and later another blast happened just 200m away.
Sources said that just before the blasts, a Swedish news agency received a message denouncing Sweden's military presence in Afghanistan and threatening deadly attacks.
The letter in Arabic and Swedish said, "Our acts will speak for themselves. Now your children, your daughters and your sisters will die as our brothers, our sisters and our children are dying," Swedish news agency TT reported.
Swedish Foreign Minister Carl Bildt tweeted in his Twitter account that it was an terrorist attack.
"Most worrying attempt at terrorist attack in crowded part of central Stockholm. Failed -- but could have been truly catastrophic..." Bildt tweeted.