ASMARA - Somali opposition leaders in Eritrea rebuked African nations on Tuesday for shirking their duty to stop conflict in Mogadishu between Islamist-led insurgents and the Ethiopian-backed interim government.

Their call came amid more grenade and roadside bomb attacks in Somalia where insurgents are waging daily Iraq-style attacks on allied Ethiopian and Somali government troops.

"This is the responsibility of the African continent. It's time for African leaders to take action against Ethiopia (like) removing the African Union headquarters from Addis Ababa," Zakariya Mahamud Abdi told reporters in Asmara.

Some 400 opposition leaders, including several senior Islamists, are in Eritrea at a conference intended to form a new umbrella movement to press for the Ethiopians' exit.

The dissidents, who say they will be based primarily in Somalia after the conference, also lashed out at the AU peacekeeping force in Mogadishu.

"This contingent is part of the problem ... they are covering up the atrocities of the Ethiopians. They should be neutral," Abdi said of the 1,600 Ugandan peacekeepers there.

The AU mission was supposed to be 8,000-strong, but early offers of support from around Africa have not materialised.

In the latest violence inside Somalia, a grenade was hurled at a legislator's house, and police said three civilians died in gunfire after a roadside bomb targeted a military convoy.

In the provincial city of Baidoa, a gang stabbed to death a government soldier, police added.

Those three incidents took place on Monday night.

Gunmen also shot dead a Somali employee of the World Health Organisation (WHO) while he was driving his car in a revenge killing on Tuesday morning apparently unrelated to the wider conflict, local authorities said.

"A group of four clan militiamen killed Farah Warsame Diriye, a high-ranking WHO officer in Abudwaq because of a clan conflict," said Abdirizak Hassan Awil, chairman of Abudwaq district, north of Mogadishu.

In Djibouti, an influential Somali businessman briefly arrested over financing the Islamic Courts was said to be weighing whether to back them again or turn to the government.

Abukar Omar Adan, 72, supported the sharia courts' movement during their six-month rule of Mogadishu and most of south Somalia last year. He was detained in neighbouring Kenya after Ethiopian and Somali government troops drove out the courts at the New Year, scattering fighters and supporters.

In February, Kenya dropped an immigration case against Adan without explanation, and this weekend he showed up in Djibouti where Somali Prime Minister Ali Mohamed Gedi flew in an effort to bring him back to his homeland.

"He was not of the (Islamic) courts, he supported them morally and financially in the beginning," Adan's aide told Reuters by telephone from Djibouti. "But when they turned more destructive and uncompromising, he withdrew his support."

He added: "If the courts still stand for good things, he will support them, and if the government changes its tune and stands for good things, he will support them."

The aide said Adan, who ships commodities such as sugar and building materials to Somalia, would stay in Djibouti.

"He's not going to Asmara, Addis Ababa or Mogadishu."

Somalia's 9 million people have endured near-ceaseless instability since warlords toppled a military dictator in 1991.