About 200 Ethiopian troops with at least five pickup trucks mounted with machine guns and other vehicles moved into Wajid, a U.N. aid base, about 46 miles southeast of the Somali-Ethiopian border, at about 3 a.m. (0000GMT), several witnesses said on condition of anonymity because they feared reprisals. The soldiers took control of the town's airport from a militia serving the local administration, they said.
Arab League talks in Sudan, scheduled to resume Saturday, were aimed at easing the situation in Somalia, where the Islamist militia captured the capital, Mogadishu, from secular warlords and then consolidated their control over most of southern Somalia.
Both sides signed a temporary cease-fire agreement June 22, and the Islamists formally recognized the government, something they had previously said they would not do.
The talks fell apart Saturday when the Islamists walked out because of the Ethiopian incursion, and the government side said it would not attend until it received international guarantees that any agreement would be respected.
"The reason why we are walking out of the conference is that the Somali government has violated the accord and allowed Ethiopian troops to enter Somali soil," said Abdirahman Janaqaw, the deputy leader of the Islamic courts' executive council.
Representatives of the Islamic courts have been in Khartoum for the past week, but no government representative had shown up in the Sudanese capital.
"We will no longer stay in Khartoum and, although the delegates of the government have not arrived in Khartoum, we will walk out of the conference," Janaqaw told The Associated Press in Mogadishu.
Ethiopian and Somali government officials have denied Ethiopian troops are in the country.