Somalia's interim government has voted to support a US proposal that would let east African peacekeepers deploy in the violent state.
Later, an apparent suicide bomb attack at a checkpoint outside the Somali seat of government in Baidoa killed at least four people. It is not know if the attack is linked to today's agreement.
Diplomats say Washington will soon unveil a proposed UN Security Council resolution that would lift an arms embargo to let regional troops legally enter Somalia with their weapons.
Somali lawmakers, confined to provincial Baidoa town because of rapid territorial gains by the militarily superior Islamists, voted overwhelmingly yesterday to support the plan.
The proposed UN resolution has prompted debate about whether it would help stabilise Somalia, as the United States and Britain hope, or cause a broader conflict, as European Union experts and a major international think-tank have suggested.
The Islamists - who threaten the government's authority after seizing the capital Mogadishu and much of the south in June - bitterly oppose foreign fighters operating in Somalia.
"The whole world knows the passage of this resolution will bring nothing but war," Ibrahim Hassan Addow, the Islamists' foreign affairs chief said.
He said it was aimed at legitimising the presence of thousands of Ethiopian troops that diplomats say are in the country to prop up the Western-backed government.
Mr Addow said if the plan was approved by the United Nations, it would spell the end of stalled peace talks between the two sides.
Analysts fear an all-out confrontation between the government and Islamists could spiral into a wider regional war, sucking in neighbouring countries.