South Africa is mulling sending the army and navy to Somalia to reinforce the troubled African Union (AU) peacekeeping mission in war-torn Mogadishu, Defence Minister Lindiwe Sisulu said on Thursday.

"As we sit here now, there has not been a specific request to us from the AU to send troops but we did commit ourselves to assisting," she told reporters in Cape Town.

"Not to deploy will be an issue...if we are not able to provide a cogent argument why we are not able to."

Sisulu said that rejecting a request by the pan-African body to deploy in Somalia could compromise South Africa's respect and standing on the continent but recognised that such a mission would come with high risks.

The AU Mission in Somalia (Amisom), has suffered significant fatalities and Uganda this month saw 76 civilians killed in twin bombings in Kampala, carried out by Somalia's al-Shabaab extremists in retaliation for its leading role in the force.

AU leaders this week agreed to boost the 6 000-strong mission, which is also in dire need of equipment, by another 2 000 soldiers.

"It is a very different kind of war," Sisulu said, comparing Somalia with South Africa's longstanding involvement in peacekeeping in the Democratic Republic of Congo and Sudan.

"The South African public would need to understand that this is in another realm."

Deputy Defence Minister Thabang Makwetla pointed out that the existing deployments were peacekeeping missions but that in Somalia, South African troops would find themselves in the role of "peace enforcing" as Amisom tries to shore up the fragile transitional government against insurgents, notably the al-Qaeda linked al-Shabaab.

Sisulu said that the matter was with President Jacob Zuma and added that she expected him to deal with it "pretty soon".

He would give Cabinet a report on the possibility of engaging in Somalia and then call in Sisulu, Makwetla and the command of the defence force to weigh the financial and logistical implications of committing troops.

Sisulu was adamant that South Africa would not foot the entire bill of any eventual deployment. "If we were ever to go to Somalia, it would be a shared responsibility."

The minister said that she had no doubt that the South African military was up to the task, but was concerned about whether Pretoria could commit more troops to African missions given its involvement in the DRC, Sudan and the Central African Republic.

"Yes, South Africa is combat ready but whether we have the numbers to deploy on other peacekeeping missions is another matter."

She added that any deployment would entail both the army and the navy, saying it meant little to help tackle the problem of piracy of the Somali coast without trying to restore political stability to Mogadishu.

"Patrolling the waters won't stop the problem. The most important thing is to support the government of Somalia."

Sisulu added that she was concerned about how the public would respond to a deployment in one of Africa's most troubled nations.

She said that she was hugely relieved that the call on African nations to bolster the force came after the 2010 FIFA World Cup, as South Africa could not have run the security risk of tackling the issue while hosting the world's biggest sporting event.

"We did not want to get into this discussion until the World Cup was over."

The al-Shabaab and Hisb-ul-Islam militia groups have been battling Somalia's government for three years and control most of southern and central Somalia, and sections of Mogadishu.

The country has not had a functioning government since the ouster of dictator Mohamed Siad Barre in 1991.