More than a dozen prominent Zambians have been arrested in the country's biggest internal security crackdown in years, following the discovery of an alleged plot to overthrow President Kenneth Kauda's government, police sources said yesterday.

The arrests followed imposition of a dusk-to-dawn curfew in the capital and most of the country's other major towns, and deployment of troops west of Lusaka, where a heavily armed gang was sighted recently.

The gang, variously estimated to number between 50 and 200, clashed with security forces south of Lusaka 10 days ago but since has broken up into smaller groups believed to he heading northwest toward the Zairian border.

Roadblocks have been thrown up around Lusaka and a major military exercise appears to be under way. Correspondents who visited the area saw steel-helmeted troops deployed at road-blocks and a helicopter flying low over the bush.

The government has not officially linked the arrests with the gang, but police sources said they possessed information that suggested a coordinated attempt to overthrow the government. Among those picked up in police raids during the past two days are four men who served Kaunda in senior government posts before leaving to take up jobs in the private sector.