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Security forces in Nepal were on high alert Monday 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 neighborhoods, while the third one was a few hours later.

Police said they suspect that a group that once split from the ruling Communist party was responsible for the blasts because its members have been protesting the arrests of their supporters.

The first explosion occurred in northern Kathmandu, killing two people and wounding five, police said. The second blast was in a house in the central part of the city, killing one and wounding one.

Police believe the men in the house are linked to the outlawed group, which is known for violence. They said they found pamphlets from the group at the second explosion site.

The areas around the two blast sites were quickly closed by police and the wounded were taken to hospitals.

Police said a third explosion wounded two people who they believe were members of the group transporting the explosive device.

The splinter communist group split from the Maoist party, which fought government troops from 1996 to 2006, when its members gave up their armed revolt to join a peace process and mainstream politics.