(Recasts with violence)

KATHMANDU, May 21 (Reuters) - Police lobbed tear gas shells to break up an anti-Maoist rally during a day-long strike in the Nepali capital on Wednesday in a protest over the killing of a businessman by Maoist former rebels, police and organisers said.

Ram Hari Shrestha, a restaurant owner, was abducted and killed in southern Nepal earlier this month. Maoists said some of their members killed him, but they were not acting on the party's orders. They have vowed to bring the culprits to justice.

Schools and businesses were shut in Kathmandu on Wednesday, as protesters set up road blocks and burned tyres at some intersections to stop vehicles.

"The government must investigate the killing and punish the culprits," Shrestha's wife Ramila said. "The Maoists must publicly apologise."

Shrestha's family and local residents called for a day's strike, which was backed by the main political parties.

Police said some protesters pelted several vehicles with stones for defying the strike. They also clashed with Maoists in some areas.

The killing of the businessman came a month after the former rebels emerged as the biggest group in elections held last month for a special assembly. They are trying to head a new government.

The assembly is due to hold its first meeting next week and is expected to declare an end to the centuries-old monarchy, a major condition of the 2006 peace deal ending a decade-long civil war.

Main political parties in the Himalayan nation accuse the Maoists of continuing violence and intimidation, despite joining electoral politics. (Reporting by Gopal Sharma; Editing by Bappa Majumdar and Alex Richardson)

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