Mogadishu - A senior leader of a Somali Islamist insurgent faction has defected to the government side with his militia, bringing a boost to embattled government forces.

Sheikh Yusuf Mohamed Siyad Indha Adde, who was the defence chief of the Alliance for the Re-liberation of Somalia and the leader of a faction of Hizbul Islam - one of the groups fighting the government - said Sunday he saw no reason to keep fighting.

"There is no reason to attack this government since it has decided to implement Islamic law," Indha Adde told reporters in Mogadishu on Sunday evening. "We decided to defend this government."

Indha Adde and the co-leader of the faction, Sheikh Hassan Mohamed Amey, are believed to command around 200 fighters and a dozen armed vehicles.

Despite the defection of Indha Adde, who last week met Sheikh Sharif as fighting raged in Mogadishu, the new regime appears to be hanging on by its fingernails.

Insurgent group al-Shabaab, which has been fighting alongside Hizbul Islam, took control of Jowhar, a key strategic town north of Mogadishu, on Sunday.

Prior to taking the town, al-Shabaab overcame the pro-government Islamic Courts Union (ICU) militia in Garasaley, 25 kilometres south of Jowhar.

Jowhar, which is 90 kilometres from Mogadishu and is the hometown of Sheikh Sharif, links Mogadishu and central Somalia.

Heavy fighting has engulfed northern Mogadishu for the last ten days as insurgents push to end the short reign of President Sheikh Sharif Sheikh Ahmed.

Almost 150 people, many of them civilians, have been killed in the fighting. Hundreds more have been injured. Tens of thousands of civilians have also fled Mogadishu.

Sheikh Sharif, a moderate Islamist, has implemented sharia law and has been attempting to build bridges with the warring groups.

However, the militants say he is too close to the West.

Sheikh Sharif, who worked alongside many of the insurgents when his ICU briefly ruled Somalia in 2006, came to power earlier this year as part of a Western-backed peace process.

The UN has condemned the push and said it is a desperate measure aimed at derailing Sheikh Sharif's attempts to build bridges and bring peace to Somalia.

Eritrea has been accused of arming the insurgents, and the United Nations and the United States have called on Eritrea to stop interfering in Somali affairs.

The insurgency has claimed the lives of around 16,000 people, mainly civilians, since early 2007, kicking off after Ethiopian troops invaded to oust the ICU. Ethiopia pulled its forces out in January this year.

The resultant insecurity has helped feed an explosion of piracy in the Gulf of Aden.

Somalia has been embroiled in chaos since the 1991 ouster of dictator Mohamed Siad Barre, and is widely regarded as a failed state.(dpa)