There were no immediate reports of casualties.

The mobilisation caps weeks of unrest by Opposition demonstrators which has paralysed the government of this tiny mountain kingdom surrounded by South Africa. The Opposition has charged that the May elections swept by the Lesotho congress Party were rigged.

Some 600 troops, at the request of Lesotho's prime minister entered the kingdom at 5 am (local time), the South African Press Association said.

SABC radio reported gunfire outside the palace of King Leksie III involving the troops and dissident army troops.

A faction of the army rebelled eleven days ago, deposing the leadership -- apparently loyal to the government -- and the new commanders had refrained from restoring order in the streets.

Hundreds of protesters have camped on the groundsof the royal palace of this impoverished country of two million people. Gunfire was heard in the capital's main military barracks.

Lesotho asked for the intervention under the auspices of the Southern African Development Community.

``The aim of the intervention is to restore stability as quickly as possible and to withdraw from Lesotho as soon as this has been achieved,'' the statement said.

South Africa's safety and security minister Sydney Mufamadi said in Pretoria yesterday that such an intervention could not be ruled out if the Lesotho government was threatened.

Lesotho's Prime Minister, Pakalitha Mosisili, acknowledged yesterday that the government was not in control of the army and said intervention by foreign troops ``could be a very last resort''.

Government offices and parliament have been paralysed by weeks of demonstrations and strikes.

A SABC radio reporter said yesterday that senior government officials had gone into hiding, including foreign minister Tom Thabane. Opposition militantshauled teachers and children out of schools, the reporter said.

The intervention follows fruitless efforts by South African mediators over the weekend to bring the government and opponents together in talks.

A report by a commission of representatives from South Africa, Botswana and Zimbabwe last week cited ``serious concerns'' about the voting, but did not suggest that the election be invalidated.