The short video also showed armed men making plans and training to carry out attacks.
The group's self-proclaimed spokesman also said that the African Union should not send troops to support the Ethiopian military which has deployed in Somalia to support the countrys' weak interim government.
"We call on the African countries to refrain from sending troops to Somalia, as by doing this they legalize the Ethiopian occupation, harm the Somali issue and get themselves involved in a dispensable trouble," he said.
Cargo plane 'shot down'
Separately, the government of Belarus said that a privately-owned Belorussian cargo plane that crashed north of Mogadishu, the Somali capital, on Friday, had been shot down.
"The plane was shot down," Kseniya Perestoronina, a transport ministry spokeswoman said in Minsk, the Belorussian capital.
She said that the large Ilyushin-76 aircraft, in Somalia to assist struggling African peacekeepers, was hit at a height of 150 metres and that all eleven passengers and crew had died in the crash.
All eleven crew and passengers aboard died when the plane crashed [AFP] 
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The statement appeared to confirm initial reports from both a local Somali radio station and an Islamist web site that a missile had hit the Russian-made aircraft just after takeoff from Mogadishu on Friday afternoon.
However Mohamed Mahamud Guled, Somalia's interior minister, said that although investigations were continuing, the crash was due to a technical fault.
"The plane took off at around five o'clock and as soon as it reached 10,000 feet altitude, the pilot reported an engine problem in engine number two and said he would turn back to the airport," he told a news conference in Mogadishu.
The plane had brought a team to fix another Ilyushin lying damaged at Mogadishu airport after flying in peacekeepers.
That plane caught fire on the runway in an incident the AU said was a technical fault, but Islamists said was a missile attack.