'Situation not ripe'
Ban said on Wednesday it would be too risky to send UN peacekeepers.
"The situation is not ripe, the conditions are not favourable ... If there is no peace to keep, peacekeeping operations are not supposed to be there," he said.
He said the first priority should be to strengthen the African Union force known as Amisom.
First deployed in March 2007, it is authorised to have 8,000 troops, but now includes only 2,600, mostly Ugandans and Burundians.
The US and Somalia want a UN peacekeeping force to take over duties from Amisom, which has so far proved ineffectual.
Ethiopia is planning to withdraw their troops, which are backing Somalia's government, early next year.
There are fears that the violence in the country will increase unless more peacekeepers are sent soon.
Somalia has been wracked by civil war for 17 years.
A previous UN peacekeeping mission in Somalia pulled out in 1995, after two US army Black Hawk helicopters were shot down and 18 US soldiers were killed in a battle in 1993.
Eleven people were killed on Wednesday in fighting between al-Shabab fighters and Ethiopian forces in the capital Mogadishu, witnesses said.
Al-Shabab controls most of south and central Somalia and carry out almost daily attacks on government troops and their Ethiopian allies.
"We shall continue the war until foreign troops get out of the country," Sheikh Muktar Robow Ali Abu Mansoor, an al-Shebaab spokesman, said.
He said many Ethiopian soldiers had been killed in the fighting.