John Holmes, UN under-secretary-general for humanitarian affairs, said on Tuesday that "recent administrative directives" by Somalia's interim government had further obstructed aid efforts.
He was speaking after a meeting between Somali officials and UN aid agencies in the southern Somali town of Baidoa on Monday.
Holmes told the UN Security Council that roads and airstrips had been closed, the authorities had failed to clear food shipments for distribution and aid workers faced harassment at checkpoints.
However, he said that during Monday's meeting the Somali government officials supported the delivery of aid.
Holmes said the country's health minister had been named to co-ordinate with aid providers and all airstrips were now open to them.
"I very much welcome this, if it is confirmed, and look forward to it being translated into real actions on the ground to enable humanitarian staff to access relief supplies.
"The reassurances we received yesterday were good as far as they go, but they have to be translated into action," he said.
News of the promise to provide a clear path to aid for civilians came amid more violence in Mogadishu.
At least four people died on Tuesday in a a car bomb blast in the Somali capital as battles between government-backed forces and fighters loyal to the Union of Islamic Courts (UIC) raged for a seventh day.
Ethiopian troops backing the government were attacked by a suicide bomber and tank fire killed at least three people during the clashes.
At least four people were killed when a car packed with explosives detonated outside the Ambassador Hotel in the centre of the city as two Ethiopian troop trucks drove by.
|The UN estimates that at least 321,000 |
civilians have fled Mogadishu [EPA]
In Afgooye, a small town 30km west of the city, a suicide car bomber blew up at an Ethiopian military base.
"I saw the Ethiopian soldiers shouting at this car to stop, then it exploded," said a local resident, Abdi Hassan.
Ethiopian troops ran from the scene, Hassan said, adding that he thought there were few casualties.
Ethiopian tanks also pounded positions in northern and southern Mogadishu in a bid to weaken fighters.
At least three people were killed and six others wounded when a mortar crashed into a concrete building sheltering about 20 people in Tawfiq in southern Mogadishu, witnesses said.
Mutilated bodies lay rotting in the streets in northern suburbs on Tuesday, with fighting blocking access for aid workers.
Yusuf al-Azhari, a Somali political adviser, told Al Jazeera that the government evicted what he called "terrorist groups" from one of the two districts in Mogadishu.
"Mogadishu is divided into 16 districts. Two of the districts were occupied by the so-called union courts terrorists, who are supported by al-Qaeda and terrorist groups around the world.
"The government is now fighting the group to evict them from those two districts. The government forces have already succeeded in evicting them from one place."
Al-Azhari defended the presence of Ethiopian forces in Somalia, saying there are there at the invitation of the Somali government.
Ibrahim Addou, secretary of foreign affairs at the Islamic Courts Union, said the group had no relations with al-Qaeda.
"These accusations are cheap terms used for fund-raising purposes by Ethiopia. Somalia is under the Ethiopian occupation, which is being resisted by the Somali people."