Numerous governments and peace initiatives have failed to end the conflict that has defined Somali politics since a clan uprising overthrew Mohamed Siad Barre, then president, in 1991.
Holmes, speaking in southern Mogadishu, said: "There has been a response, but we need to do more. It is very hard for aid agencies to operate in Somalia."
Holmes, who is on his second visit in a year to the country, said numerous checkpoints, where aid groups are forced to pay for passage, add to the difficulties of helping a population displaced by fighting.
Few aid agencies have been able to establish permanent operations in the country, but more than one million people have fled the fighting.
Nur Hassab Hussein, the recently installed interim prime minister, said he was ready to discuss "power-sharing" with opposition leaders.
| A civilian is treated after the fighting in Jowhar AFP] |
However, Hussein's new cabinet has already started to show cracks, with four members announcing their resignation on Monday, a day after being sworn in.
Hassan Mohamed Nur, the home security minister, Abdikafi Hassan, the state trade minister, Sheikh Aden Maden, the state reconciliation minister, and Ibrahim Mohamed Isaq, the state planning minister, said they had not been consulted on their appointments.
Hussein, who is seen as a political novice, had sworn in a 73-member team, including 31 ministers, 11 state ministers and 31 assistant ministers, excluding ministers who had served under his predecessor.
Hussein was guided by a law which says that the four main clans and one minor one should be represented in government on an equal basis.
Ali Mohamed Gedi resigned as premier on October 29 after a long-running feud with Abdullahi Yusuf Ahmed, the president, who had accused him of failing to end the fighting, draft a new constitution or bolster federal government.
The interim government brought in Ethiopian forces to fight the Union of Islamic Courts which had gained ground in 2006. The ongoing clashes have displaced at least 600,000 people from Mogadishu since February and hampered the delivery of relief aid.
Heavy battles last month drove out a further 200,000 people from the capital, according to the UN refugee agency.
Much of the fighting since the start of the year has been in Mogadishu.
But on Monday, fighting started in Jowhar, 90km north of the capital, between members of the security forces over unpaid salaries.
According to residents and local officials, at least three people died and more than 10 were wounded.
The World Food Programme (WFP) also announced on Monday that the number of people it had been providing daily meals to in Mogadishu has reached 21,000 people. The body hopes to feed up to 50,000 people every day.
The agency launched the operation on November 25.
"The depth and scale of the crisis in Somalia is extremely alarming," Peter Goossens, WFP's Somalia country director, said.