Security forces in Nepal are on high alert amid a general strike called by an outlawed communist group suspected in a series of explosions that killed four people and wounded seven more in the capital.

Schools and main markets remained closed on Monday in Kathmandu while traffic was thin during rush hour.

The group had called for a nationwide general strike to pressure the government in releasing their detained members.

Police official Shyam Lal Gyawali said authorities were investigating Sunday's blasts. The first two explosions occurred within minutes apart in two Kathmandu neighbourhoods, while the third one was a few hours later.