|The Islamic Party says merging with al-Shabab will create a stronger force against a weak government [Reuters]
Somalia's al-Qaeda linked al-Shabaab rebels, who have waged a three-year insurgency aiming to impose a strict form of Islamic law, merged this week with Hizbul Islam, a smaller group which had battled them for control of southern towns.
"After successive meetings, and relentless debate between the leadership of the Mujahideen al-Shabaab and that of Hizbul Islam, the day which we have been waiting for has finally arrived. The day of unity, the day of understanding and gathering and oneness," Sheikh Ali Mohamud Rage, Shabaab spokesman, said .
Between them, they control most of central and south Somalia and much of the capital, hemming United Nations-backed President Sheikh Sharif Ahmed's government into a few blocks.
Sheik Ali Mohamud Rage, a spokesman for al-Shabab, said the insurgent group would tell other armed fighters around the world that insurgents in Somalia have united.
|Abdi Aynte, an editor for the Al Jazeera English website, said the process is more a surrender than a 'merger' and poses no threat
"We are telling our mujahedeen brothers in Afghanistan, Pakistan and elsewhere in the world that we have united in one name - that is al-Shabab."
Fighters from the Hizbul Islam, the Islamic Party, have been defeated several times by al-Shabab, including a battle to control the port city of Kismayo, one of the largest cities in the country, and now a major base for al-Shabab.
Hizbul Islam, however, denied that the merger was a face-saving tactic for his group, saying the union is "a bonus for the Mujahideen and a bane to the invaders and mercenaries".
"From now on we will concentrate our power on how we can redouble our attacks on foreign invaders,'' Rage said.
The rebel groups said on Thursday, that they would increase attacks on Uganda and Burundi after tightening their grip on much of Somalia by joining forces with each other.
Uganda and Burundi have troops in Somalia as part of an 8,000-strong African Union (AU) force protecting the government.
Al Shabaab claimed responsibility for twin suicide bombings in the Ugandan capital Kampala on July 11
which killed 79 people watching the World Cup final between Spain and the Netherlands on television.
The bombings were al-Shabab's first attack outside Somalia and heightened concerns about the group's interest in international attacks.
Burundi said it was increasing security around the holidays.
The AU force also said it was not cowed by threats.
Kenya, Uganda and Tanzania have issued security alerts after a grenade exploded at a bus depot in Nairobi on December 20.
Uganda said on Monday, that it had received intelligence reports that an al Qaeda-linked group was planning to hit the east African country during the festive season.
In 1998, al Qaeda car bombs hit the U.S. embassies in Tanzania and Kenya, killing 224 people.
More than 21,000 civilians have been killed in Somalia since the al Shabaab insurgency started in 2007.
Talk of major offensive
The UN-backed Somali government has been promising a major offensive to stamp out al-Shabab for more than a year but the fighters still control three quarters of the country.
The two groups have previously fought together against government forces despite ideological differences and the recent clashes.
The Islamic Party has in the past condemned al-Shabab's use of such tactics as suicide bombers and summary executions.
Sheik Hassan Dahir Aweys, the founder of the Islamic Party, also criticised al-Shabab's public pledging of allegiance to Osama bin Laden.
The Islamic Party has about 2,500-3,000 fighters and was widely seen as having a more nationalist agenda than al-Shabab, which has been heavily influenced by Wahhabi Islam ideology.
Both al-Shabab and the Islamic Party have been plagued by factionalism.
The insurgents hold most of south-central Somalia and much of the capital city, Mogadishu.
So far they have been unable to seize the port, airport or key government installations, which are protected by an African Union peacekeeping force.
Somalia has not had a functioning government for 20 years.