Ethiopian troops have apparently crossed over into Somalia, weeks after Kenya launched its own incursion into the country in pursuit of al-Shabab militants. Some analysts say the Kenyan operation can succeed only if Ethiopia cooperates.  

Witnesses said this week they had seen Ethiopian troops cross the border into Somalia.  The Ethiopian government denied the move, but the Somali defense minister confirmed it and said the troops would work with Somali government forces.

An Ethiopian invasion in Somalia will open up another front in the fight against al-Shabab, but analysts say Ethiopia's presence could also give al-Shabab a life line.

Tension has historically run high between Ethiopia and Somalia and reached a new high five years ago with an Ethiopian invasion that targeted Islamist militants in the capital.

Al-Shabab gained support in Somalia by fighting off Ethiopian forces during that time, using anti-Ethiopian sentiment to rally support for their own insurgency.

Abdiwahab Sheikh Abdi Samed, a Somali political analyst with Southlink Consultants in Nairobi, says  Ethiopia would be better off working with the African Union peacekeeping force, AMISOM, that backs Somalia's government in Mogadishu.

“Somalia and Ethiopia, they have been long time enemies to each other, so trusting Ethiopia again it will take time," said Samed. "But if they come under the umbrella of AMISOM, it is better than what they are doing right now.”

This week's Ethiopian incursion follows a Kenyan military operation targeting al-Shabab in southern Somalia that began more than a month ago.

The Kenyan government has called on the international community to assist in the operation. Kenya, meanwhile, says it is considering contributing troops to the AMISOM mission.

But Samed says Somalis are concerned to see their neighbors sending troops into the country. He notes there has always been tension between Somalia and the countries that it shares a border with, including Kenya and Ethiopia.

“The front line states are the ones who are ready to send troops into Somalia," added Samed. "It’s better African Union peace force to come from Ghana, Sierra Leone, Nigeria, and Malawi and so on. But still there is a lot of suspicion about front line state.”

There is also a lot of concern about the incursions among Somalis on the ground.

Abdifatah Hassan Farah is the editor of Radio Galgudud in the Gurieel Galmudug region of central Somalia. His station reported a heavy presence of Ethiopian forces in and around the town last week.

Farah says Ethiopian troops are still positioned in the region, but that he does not know what their mission is, or where they are going next.