Holmes told the UN Security Council on Tuesday that none of the sides in the deadly fighting that has raged in Mogadishu in recent weeks was respecting the rules of war or making any allowance for aid operations.
"Civilians in Mogadishu are paying an intolerable price for the absence of political progress and dialogue and the failure of all parties to abide by the rules of warfare," said Holmes, also the UN's Emergency Relief Coordinator.
Separately, the European Union (EU) has reiterated its concern regarding the humanitarian situation in southern Somalia, and has appealed to Somali President Abdullahi Yusuf to personally intervene as a matter of utmost urgency.
"In line with recent statements by this Presidency, by Commissioner [Louis] Michel and High Representative [Javier] Solana, and by the International Contact Group meeting in Cairo, the European Union wishes to reiterate its concern regarding the humanitarian situation unfolding in southern Somalia, and to appeal to you personally to intervene as a matter of utmost urgency," said Walter Lindner, the EU president and Germany's representative, in a letter on Friday.
Lindner called on the Transitional Federal Government (TFG), under international humanitarian law and its duty to protect Somali citizens, "to take urgent and transparent measures to contribute to putting an end to the unacceptable practices and to allow relief agencies full and unfettered access to the needy".
On Wednesday, clan elders and Ethiopian commanders met for the first time in Mogadishu since the latest round of fighting started eight days ago.
"Our representatives are meeting with Ethiopian commanders as we speak," Abdullahi Sheikh Hassan, a spokesman for the Hawiye elders told IRIN.
Hassan said no agreement had been reached so far, but the two sides were discussing how to put in place a new ceasefire. Fighting in the city had died down, "with minor skirmishes going on", he said.