Lesotho PM Thabane's coalition folds, he leaves on May 22 -speaker

National Assembly Speaker Sephiri Motanyane announced the collapse of his governing majority and said Thabane, 80, would have to step down by May 22. Thabane's spokesman did not immediately respond to a request for comment.

Thabane has been under pressure to resign over a case in which he and his current wife are suspected of conspiring to murder his ex-wife. His current wife, Maesaiah has been charged while Thabane has been named as a suspect though has yet to be formally charged. They both deny any involvement.

The case has divided his party and triggered sporadic unrest. Thabane had promised to retire, but had been dragging his feet on when to do so.

"We have verified that the four-party coalition agreement has been terminated and there is a formation of a new government," Motanyane said.

Sam Rapapa, deputy chairman of Thabane's All Basotho Convention (ABC) party, said all parties had provisionally agreed on Finance Minister Moeketsi Majoro to replace Thabane.

"Thabane is now a caretaker prime minister until May 22 when a new prime minister is sworn in," Rapapa said.

Members of the ABC, opposition parties and South African mediators have been pressing Thabane to leave. King Letsie III last week assented to legislation that prevented Thabane from dissolving parliament and calling an election in the event of a vote of no confidence against him.

Political instability frequently boils over in Lesotho, which has experienced several coups since independence from Britain in 1966. Its conflicts often draw in South Africa, whose central mountains encircle the tiny, mountain kingdom and supplies it drinking water. (Reporting by Reporting by Marafaele Mohloboli; Writing by Tim Cocks; Editing by Mark Heinrich)