Ethiopian military personnel landed at a Somali airbase on Saturday after Ethiopian troops took control of the airport in the southwestern Somali town of Wajid, residents and aid workers said today.
The troops seized the air base from gunmen serving the local authorities overnight and met with no resistance, the sources said.
Two helicopters carrying Ethiopian forces landed this afternoon.
Earlier today Somalia's Islamists refused talks with the government, blaming an incursion by Ethiopian troops sent to defend the interim administration's limited authority, Islamic officials said today.
"We do not negotiate with a government which is being helped by the enemy of Somalia," senior Islamist leader Sheikh Sharif Ahmed said in a letter to Islamist delegates to the talks.
The letter was quoted in a press statement by the Islamist movement, which is threatening the authority of a fragile government formed in 2004 to steer the Horn of Africa nation from anarchy to peace.
The move came as several residents said more Ethiopian forces and armoured vehicles arrived in the Somali government's provincial base of Baidoa overnight to help guard the parliament, presidential palace and airport.
A second round of talks to prevent an increasingly belligerent standoff between the two sides from spiralling into war was due to take place in the Sudanese capital Khartoum.
"The problem now is the conflict between Ethiopia and the Islamists," said Sudanese foreign ministry spokesman Jamal Ibrahim.
An Islamist delegation was in Khartoum, but the government's was not, he added.
Diplomats fear Somalia is on the verge of war after Islamist militia moved their closest to the government's provincial base in Baidoa this week, and witnesses said Ethiopian soldiers had poured across the border to protect the government.