African Union peacekeepers killed in Somalia
Four African Union peacekeepers were killed when a mortar hit Somalia's presidential palace, officials say.
It is not clear if any Somalis were hit by the shells, fired as Islamist insurgents continue to battle government forces.
Those killed were from Uganda, one of just two countries to have sent troops to Somalia to help the government.
Last month, at least 76 people were killed in Uganda in bombings which a Somali group said it had carried out.
The battle for control of Mogadishu has intensified in the past week.
Last Monday, a suicide attack on a hotel killed at least 32 people, including six MPs.
The Islamist group al-Shabab said it had carried out the attack. Last month, al-Shabab said it was behind two bombings in the Ugandan capital, Kampala, in which more than 70 people died.
Al-Shabab, which has links to al-Qaeda, controls much of southern and central Somalia, while the government - backed by the 6,000-strong African Union peace force - is confined to a few pockets of the capital.
A spokesman for the AU peacekeepers told the BBC the mortar attack was of little significance.
"These opposition groups fire from positions three to four kilometres from our positions. It was a pure coincidence that the mortar was able to kill four and injure eight of our soldiers," Major Barigye Bahoku said.
He added that fears that al-Shabab fighters were going to close the road to Mogadishu's airport in their latest offensive were also unfounded.
"They cannot do it as long as we [the AU] are present. Every single Ramadan [Muslim holy month], these guys come up with these threats," he said.
"In 2008 they said the airport would never function again. This year they say they will chase away the brotherly African Union peacekeepers.
"They just make a lot of noise and that noise will never materialise to anything serious."
But on Monday, President Sheikh Sharif Sheikh Ahmad appealed for more international help to contain the "evil al-Qaeda-al-Shabab alliance".
Last month African leaders agreed to send an extra 2,000 troops to Mogadishu.
Meanwhile, there are reports that Ethiopian troops have been crossing into Somali over the last two days.
An unknown number of Ethiopians, with armoured cars, have carried out operations against al-Shabab insurgents in an area 20km (about 12 miles) inside Somalia towards the central town of Beledweyne.
Al-Shabab has been fighting a pro-government militia for control of Beledweyne in recent months.
Ethiopia sent between 5,000 and 10,000 troops into Somalia in support of the transitional government at the end of 2006.
They finally withdrew in 2009 after MPs chose Mr Ahmad, a moderate Islamist, to replace President Abdullahi Yusuf Ahmed, who had been a close ally of Ethiopia.
Somalia has experienced almost constant conflict since the collapse of its central government in 1991.