A 45-year-old woman has also been taken to hospital with injuries, according to reports.
An object now believed to be a hand grenade blew up after a 60-year-old man picked it up from the ground, leaving him in a serious condition.
Police activity near Varby Gard metro station
Two people have been injured after an explosion outside a metro station in Stockholm.
He says a woman with the man received minor wounds to her face and both legs from the blast.
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"This had then exploded and hurt the man seriously".
Police checked in and around the subway station after the blast to make sure there were no other explosive devices. "I don't dare imagine what would have happened if one or several children had found the hand grenade".
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The Swedish tabloids Aftonbladet and Expressen claimed the device may have been a hand grenade but Olsson dismissed that as speculation.
The Varby Gard station was cleared on Sunday and the Stockholm subway was partially shut, with replacement buses serving part of the route on the affected line.
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