A home-made bomb was thrown at a group of people who had been standing at a Moscow bus stop and four people were injured in the resultant explosion, according to reports.

RIA Novosti said police have launched an investigation into what was described as 'a case of hooliganism'.

The four injured include a man and three women. Earlier, it was reported that only three women were injured in the attack at a bus stop on Pokrovka Street in the center of Moscow.

Three of the injured have been hospitalised in the Institute of Emergency Care at Sklifosovsky, the Department of Health in Moscow reported, adding that the fourth victim refused hospitalization. None of the injuries are life-threatening, authorities say.

TASS news agency said a self-made firecracker thrown by an unidentified person from the window of a passing car or a nearby building might have caused the blast, quoting local police department spokesman Andrei Galiakberov.

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