Somalia's Shebab fighters have warned they will "cut the throat" of members who shift allegiance from Al-Qaida to Islamic State, amid reports some factions have already been punished for doing so.

"If anyone says he belongs to another Islamic movement, kill him on the spot," top Shebab official Abu Abdalla, said in a radio broadcast Monday. "We will cut the throat of any one... if they undermine unity."

A Somali member of parliament has died hours after he was shot and wounded when gunmen sprayed his car with bullets, the prime minster said Sunday.

MP Mohamed Ahmed Gurhan was hit by gunfire several times as he traveled through the capital Mogadishu on the way to parliament on Saturday, the latest attack targeting members of parliament.

Somalia's president called on Islamist Shebab fighters Wednesday to surrender amid reports factions have shifted allegiance from Al-Qaida to Islamic State.

Both militant franchises are "destroyers", President Hassan Sheikh Mohamud said in a statement, saying he had followed "with interest the now-public dispute within Al-Shebab, over whether to swear allegiance to Al-Qaida or the Islamic State."

Somalia's Shebab Islamists have threatened to "welcome with bullets" British soldiers due to be deployed in support of an African Union force.

British Prime Minister David Cameron said last month that up to 70 troops would be sent to Somalia to support soldiers of the African Union Mission in Somalia (AMISOM) without giving a date.

Finland on Wednesday temporarily froze its decisions on Iraqi and Somali asylum claims, to assess whether more applicants could be sent back home following a surge in arrivals from the two restive countries.

"The Finnish Immigration Service freezes its decision-making on Iraqi and Somali asylum claims for the time being. This is due to the ongoing assessment of the security situation in Iraq and Somalia," the service in charge of handling the applications said in a statement.

Britain is to send dozens of troops to Somalia and possibly South Sudan to train soldiers and boost security in the region, Downing Street said Monday.

Around 70 troops will go to Somalia, where the al-Qaida-affiliated Shebab is fighting to overthrow the internationally-backed government in Mogadishu protected by 22,000 African Union troops from Burundi, Djibouti, Ethiopia, Kenya and Uganda.

Five people were killed and 13 wounded on Monday when a car bomb exploded near a heavily-guarded complex housing the offices of Somalia's president and its prime minister in Mogadishu, a security official said.

There were no immediate reports of anyone attempting to enter the complex, and there was no claim of responsibility.

Somalia's Islamist Shebab insurgents claimed Wednesday to be holding Ugandan troops hostage after an attack last week, although Kampala has said all its troops are accounted for.

"The soldiers are in the mujahedeen jail," Shebab spokesman Abdiaziz Abu Musab said in a statement broadcast on the Al-Qaeda-linked group's Radio Andalus, but gave no further details on the alleged hostages.

At least 50 African Union soldiers are believed to have been killed and another 50 are missing after Shebab militants overran a military camp in southern Somalia on Tuesday, according to Western military officials.

"It is assessed that at least 50 AMISOM troops died," said a briefing note sent to diplomats by Western military officials and seen by Agence France Presse. It said that in total around 100 soldiers were "unaccounted for" after the attack.

Somalia's Al-Qaida-affiliated Shebab militants rammed a suicide car bomb into an African Union base Tuesday before storming the compound, with witnesses reporting many dead, although the AU insisted it had fought off the attack.

Eye-witnesses said the Shebab had taken over the camp and were looting the weapons stores, but the AU force in Somalia (AMISOM) insisted it was in control of the base.