MOGADISHU - A Somali rebel group has told the Horn of Africa nation's embattled president to resign and said hardline Islamists had succeeded where the government had failed, in establishing order in areas they controlled.

Hizbul Islam, which has waged a three-year insurgency against the fragile interim government alongside the al Qaeda-linked al Shabaab group, urged Somalia's Muslims to unite and join the Islamists' struggle.

Hardline Islamists control vast tracts of south and central Somalia and much of the capital Mogadishu, hemming the government into just a few blocks manned by African Union (AU) peacekeepers.

In recent days, the militants have intensified their offensive on government targets and killed four Ugandan peacekeepers deployed near the presidential palace.

Bent on imposing a strict version of sharia, Islamic law, on the nation, the militants routinely carry out stonings and amputations and have banned football, music and school bells in areas they control. They claim to have restored law and order.