(Adds rebel group claiming responsibility, details)

KATHMANDU, Jan 18 (Reuters) - At least seven people were killed and 22 injured on Friday after a bus exploded in flames in southern Nepal, police and local media said.

A rebel group fighting for regional autonomy claimed responsibility, local media reported. Police said they were unable to confirm this.

The Terai Army, one of many rebel groups fighting for the autonomy of the Terai plains along Nepal's border with India, called the local Radio Birgunj station shortly after the fire, the radio station and other media reports said.

The group said they attacked the bus for defying a transport strike called by the group. Details of how the attack was carried out were unclear.

Nepal only recently surfaced from a decade-long civil war in which Maoist rebels sought to topple the monarchy. The Maoists agreed to a peace deal and joined mainstream politics in 2006.

Since then, Nepal's southern plains have suffered ethnic tensions with several armed groups seeking regional autonomy. Scores of people were killed in violence in the area last year, which remains the biggest security worry ahead of national elections in April.

The bus was travelling from Janakpur to Birgunj in the Terai plains when it caught fire about 80 km (50 miles) southeast of Kathmandu, a police officer said.

Police said they had removed seven badly charred bodies, including a woman and a child. They have detained a member of the bus's staff for interrogation, but said the driver of the bus had run away.

In September, the Terai Army claimed responsibility for a series of bombs in Kathmandu which killed three people. (Reporting by Gopal Sharma; Editing by Richard Meares)

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