More than half of the population of Mogadishu has fled
At least 20 people have been killed after shells were fired at the main market in the Somali capital, Mogadishu, witnesses say.
Islamist insurgents fired mortars at the presidential palace from positions in the Bakara market, a BBC correspondent in the city reports.
Government troops and their Ethiopian allies responded and a shell landed in a busy part of the market.
Meanwhile, a landmine has killed a UN driver in the southern port of Merca.
An Italian and a Somali official who were also in the vehicle are being treated for their injuries, which are not life-threatening, a local doctor said.
Separately, a BBC reporter said two government soldiers had been killed in an attack at Mogadishu's strategic K-4 junction, where some African Union peacekeepers are stationed.
Heavy rain and flooding have also forced thousands of people in refugee camps on the outskirts of Mogadishu to return to the city, UN aid workers say.
The BBC's Mark Doyle recently visited the camps and says people were living under hopelessly flimsy shelters made from sticks covered in cardboard or rags.
The latest attacks come as the UN has started to pull out its foreign staff from the town of Baidoa.
Well placed humanitarian sources who asked not to be named have told the BBC they are leaving the town, where Somalia's parliament is based, because of fears that the violence in Mogadishu could spread.
Baidoa, a strategic town on the main road from Mogadishu to Ethiopia, is one of the few parts of Somalia under government control, correspondents say.
In the capital, Bakara trader Abdulahi Hassan said he had seen 15 bodies outside his shop.
"A mortar first landed, killing two people. Many people rushed to the scene and then as they crowded another one landed, killing 13 others on the spot," he said.
Another Mogadishu resident, Safiya Haji Nor, said the insurgents' mortar had landed on a house, killing a man and a 13-year-old child.
A further three people were killed in during the shelling, witnesses said.
Seventeen years of fighting in Somalia has left more than three million people - almost half the population - needing food aid, according to the World Food Programme.
"The situation is appalling and it is worsening with this growing insecurity," WFP spokesman Peter Smerdon told the BBC.
The latest deaths come after a coalition of 52 aid agencies issued a statement saying the international community had "completely failed Somali civilians".
The aid groups estimated that almost 40,000 people had been displaced from Mogadishu in the last few weeks, with 1.1 million uprooted in the last nine months.
Human Rights Watch said Somalia was the most ignored tragedy in the world.