By Sahal Abdulle

MOGADISHU, Dec 12 (Reuters) - Somalia's Islamist movement warned arch-foe Ethiopia on Tuesday to withdraw troops from the Horn of Africa nation within a week or face war.

The Islamists, who dominate most of the south, say Ethiopia has at least 30,000 troops in Somalia near the provincial town of Baidoa, where an internationally recognized interim government is based. Ethiopia, the West and the United Nations back the government, but its power does not extend beyond town.

"Starting today, if the Ethiopians don't leave our land within seven days, we will attack them and force them to leave our country," Islamist defense chief Sheikh Yusuf Mohamed Siyad "Inda'ade" told reporters in Mogadishu.

Addis Ababa scoffed at the threat, while the United Nations urged the Islamists not to start a war that many have been fearing for months and which could spread across the region.

"I hope they will not be the beginners of this. They should avoid statements that inflame an already critical situation," U.N. envoy to Somalia, Francois Lonseny Fall, told Reuters.

The Islamists took Mogadishu and a swathe of south Somalia in June, threatening the fragile authority of the interim government of President Abdillahi Yusuf.

Diplomats and witnesses say thousands of Ethiopian troops have crossed the border to protect Yusuf's government in and around Baidoa. But Addis Ababa only acknowledges sending several hundred armed military advisers.

"The Islamic Courts are claiming the existence of Ethiopian troops inside of Somalia to attract international attention... it's not based on fact," said Ethiopia spokesman Zemehun Tekele.

At a news conference, Inda'ade, who is considered a hardliner within the movement and has been given to inflammatory comments in the past, said there were between 30,000 and 35,000 Ethiopian troops in Somalia. That was a considerably higher figure than most witnesses or regional diplomats estimate.

TROOPS MASSING

Of those, between 6,000 and 8,000 were in Baidoa, Inda'ade said. Another 1,500 were at the Ethiopia-Kenya border with 25 trucks seeking to reach Somalia via another route, he added.

"We are asking the Kenyan government not to allow Ethiopian troops to go through their country," he said. " Kenya should resist anything that will harm our good neighborly relations."

Nairobi gave no formal response. But a Foreign Ministry source said it was "impossible" Kenya would allow Ethiopian troops to use its territory for aggressive purposes.

Addis Ababa says the Islamists are spoiling for war, while the Islamists have declared jihad against Ethiopia.

At the weekend, there were two days of clashes between pro-government troops and Islamist fighters around Diinsoor, south of Baidoa, in which several people were killed.

Forces from both sides were said by witnesses to be massing on Tuesday near the town of Tiyeglow, 140 km (85 miles) northwest of Baidoa, in preparation for a possible clash.

"We are worried. I'm hearing both the government and Islamists troops are heading for our town," local resident Batulo Ibrahim Hussein told Reuters by telephone.

The Islamists now flank the government on three sides.

With Ethiopian foe Eritrea accused of backing the Islamists by sending arms and military advisers -- a claim Asmara denies -- many fear the Somali crisis could flare into a regional war.

U.N. envoy Fall, who met the Islamists last week in Mogadishu, said he would contact them again quickly.

"We will try to convince them it is not in their interests (to fight). Those troops are not aggressive, the Ethiopians are there to protect the government," he told Reuters.

Fall said Ethiopian troops would, anyway, leave Somalia once a U.N.-endorsed African peacekeeping force arrived.

The Arab League, which has been mediating government-Islamists talks in Sudan, said another meeting scheduled for Friday looked unlikely now, though efforts were still underway to bring the sides together before Dec. 20.

"There is no way to solve the Somali issue without convening talks in Khartoum or anywhere accepted by both of them," Samir Hosni, Arab League representative on Somalia, told Reuters.

(Additional reporting by Andrew Cawthorne in Nairobi and Cynthia Johnston in Cairo)

Source: Reuters