A new terrorist group has pledged allegiance toIsisas itcontinues to expand its presence in East Africa.

A group calling itself "Jahba East Africa” announced its alliance on Thursday, hailinga "new era” in the region.

In a statement, militants gave bayah (an oath of allegiance) to Isis leaderAbu Bakr al-Baghdadiand recognised him as the "rightful Khalifa (leader) of all Muslims”.

The group’s name is previously unknown but there were hints in the statement that its supporters may previously have been part ofal-Shabaab.

Jahba East Africa criticised the group, which is linked toal-Qaedaand controls swathes of Somalia, as well as launching attacks in Kenya and other countries in the region.

"We in Jahba East Africa are advising all East Africans to leave al-Shabaab and their sponsor groups, like Al-Muhajiroun, Al-Hijra and Ansar Islam,” the statement said.

"Like Al-Shabaab the sponsor groups have not understood the binding obligation of the Khalifah (caliphate).

"We are telling the mujahideen in East Africa that al-Shabaab has now become a psychological and physical prison.

"To pledge bayah to Caliph Abu Bakr al-Baghdadi is freedom for the mujahideen in EastAfrica and opportunity to wage jihad according to the Sunnah against the enemies of Allah.”

Al-Shabab recruits walk the streets of the Somalian capital, Mogadishu. (AFP)

A spokesperson said the group was "newly created” and comprised of militants fighting in Somalia, including Kenyans, Tanzanians and Ugandans.

He said militants had been detained for pledging allegiance to Isis, adding that the statement was "on behalf all the East Africans in al-Shabaab and those that seek to open new up fronts in East Africa”.

There have been rumours of internal disputes between supporters of Isis and al-Qaeda within al-Shabaab for years, culminating in the reported creation of a pro-Islamic State faction.

Pressure to switch allegiance from al-Qaeda grew when Nigerian insurgentsBoko Haramjoined Isis in March last year and released a message urging its fellow sub-Saharan jihadists to do the same.

Hundreds of newly trained al-Shabab fighters perform military exercises (AP)

Isis leaders are understood to have approached al-Shabaab leaders themselves to make an alliance and released a series of propaganda videoscalling for the creation of "Wilayat Somalia”– Somalia province.

A memo was reportedly circulated among al-Shabaab fighters in September saying that its allegiance to al-Qaeda would not change and warning of punishments under Islamic law for any dissenters.

The move to silence pro-Isis elements appears to have failed. In a newly-created Twitter account, Jahba East Africa were calling on jihadists to join them on Friday, adding: "A new era will come to East Africa soon InshaAllah (God willing).”

Isis uses pledges of allegiance by existing terrorist and insurgent groups to establish franchises around the world.