The leader of Islamic militants who have seized much of this chaotic African nation said Tuesday that the presence of Ethiopian troops sent to bolster Somalia's weak government has scuttled any chance for peace.

Sheik Hassan Dahir Aweys, who has been accused of links to Al Qaeda, rejected a call for peace talks with the government next week and instead declared a holy war against Ethiopians.

"Until Ethiopian troops leave Somali soil, we will never negotiate with the government," he said.

Aweys' comments came as the U.N.'s special representative to Somalia, Francois Lonseny Fall, arrived to urge both sides to attend peace talks next week in Khartoum, Sudan. The government agreed to the talks after meeting with Fall in the government base of Baidoa, 150 miles northwest of Mogadishu.

"We will go to Khartoum without any preconditions," said Abdirizak Adam, President Abdullahi Yusuf's chief of staff. After Aweys' announcement, a government spokesman said talks still could go on with more moderate members of the Islamic militia.

"Aweys is a terrorist, so it not surprising that he is refusing talks," Salad Ali Jeeley said. "We hope the moderate Islamists will attend the meeting."

Fall traveled from Baidoa to the capital, Mogadishu, which is controlled by the Islamic group. Fall attended prayers with two top Islamic officials, Sheik Ahmed Sheik Sharif and Sheik Yusuf Indohaadde. It was not clear whether the men — who answer to Aweys — share his call for jihad.

Tuesday's developments were the latest in a deteriorating relationship between the Islamic militants and the internationally recognized, but powerless, government. A round of peace talks that had been scheduled Saturday fell apart when the government refused to attend and the Islamic group walked out.

The two sides reached a "nonaggression pact" in June, but the Islamic group has made clear that it sees itself as the country's main authority.

Last week, Islamic troops moved near Baidoa, the only town the government holds. The troops pulled back, but neighboring Ethiopia sent troops across the border and into Baidoa to protect the government, which has no military.

Ethiopia's move worsened tensions. The largely Christian country is the longtime enemy of Somalia, which is mostly Muslim. Somali government leaders have denied the Ethiopians are here, perhaps because they don't want to appear beholden to a traditional adversary.

Anti-Ethiopian sentiment runs high. More than 5,000 enraged Somalis packed a stadium in Mogadishu for an anti-Ethiopian rally Monday at which a top Islamic militia official said he would produce "corpses or POWs" to prove Ethiopia had sent soldiers.

Somalia has been without an effective central government since warlords toppled dictator Mohamed Siad Barre in 1991 and then turned on each other, carving much of the country into armed camps ruled by violence and clan law.

The government was established almost two years ago with the support of the United Nations to serve as a transitional body to help Somalia emerge from anarchy. But the leadership, which includes some warlords linked to the violence of the past, wields no real power.

The Islamic militia's rise has prompted concerns in the United States, which accuses the group of harboring Al Qaeda leaders responsible for deadly 1998 bombings at the U.S. embassies in Kenya and Tanzania.