The Ethiopian National Defence Force is confirming an ambush by al-Shabaab extremists on an Ethiopian peacekeeping convoy in neighbouring Somalia and says Ethiopian forces are preparing a "massive offensive" in response.A statement on Saturday rejects reports and an al-Shabaab claim that several Ethiopian troops were killed. It does not give further details on casualties.The ambush was reported as the al-Qaida-linked al-Shabaab claimed responsibility for the deadly hotel assault in Nairobi and deadly attacks on forces inside Somalia. The statement does not say exactly when the ambush occurred.Ethiopia contributes troops to a multinational African Union peacekeeping mission. It also has troops in Somalia independently under Ethiopian army command.The statement says the ambush occurred when the Ethiopian convoy was traveling Burhakaba to Baidoa in Somalia's southwest.Al-Shabaab, which formed more than a decade ago in response to the presence of Ethiopian forces inside Somalia, among other reasons, has never managed to orchestrate a major attack inside the Ethiopian heartland, though it has carried out major attacks in neighboring Kenya.In late October, al-Shabab claimed killing 30 Ethiopian troops inside Somalia. Weeks before that, Ethiopian state media outlets reported that the Ethiopian Air Force killed 70 al-Shabaab members after the extremist group tried to attack Ethiopian forces.