A Swaziland court convicted a South African man of high treason and terrorism Wednesday over a botched bomb attack against King Mswati III.

High Court Judge Bheki Maphalala found Amos Mbedzi guilty of planning to plant the bomb at a bridge of the Lozitha Royal Palace in the commercial hub Manzini in 2008.

It was intended for Africa's last absolute monarch, who was due to use the bridge for an international trip the same night, but the bomb exploded prematurely in the car they were travelling in.

Mbedzi survived with serious injuries while two others in the car were killed.

The judge also found Mbedzi had been part of the Umbane People's Liberation Army, a secret militant group linked to the People's United Democratic Movement (PUDEMO), which sought to undermine elections that year until Swaziland allowed a multi-party vote.

Political parties were banned in 1973 and voters choose candidates approved by traditional leaders and the king.

A series of small bomb blasts rattled the country in 2008, with Umbane claiming responsibility for the attacks.

Following the botched attack, the state proscribed PUDEMO and several activists went into exile.

King Mswati III has faced increasing protests in the last few months as the kingdom weathers a severe economic crisis, partly blamed on his lavish lifestyle with his 13 wives.

Authorities have resisted increased demands for democratic reforms, the latest an almost two-month long teachers' strike which has died down in the last two weeks.