Flying in for a one-day visit, Holmes was expected to press President Abdullahi Yusuf and new Prime Minister Nur Hassan Hussein for help in getting aid to thousands of Somalis uprooted by fighting between government troops and Islamist insurgents.

"There has been a response but we need to do more. It is very hard for aid agencies to operate in Somalia because of the general security situation," Holmes told reporters after landing at K50 airport, 50 kms (31 miles) southwest of the capital Mogadishu.

"There are checkpoints everywhere and aid agencies are stopped at these points and at times charged a lot of money. This is what I intend to discuss with the president and the prime minister."

In April, the interim government, which is struggling to assert its authority over a nation mired in lawlessness since 1991, promised it would clear obstacles to delivering aid after Holmes complained about red tape and restrictions.

On his second visit to Somalia this year, Holmes was due to tour camps for internally displaced families between the capital and Afgoye some 30 kms (19 miles) away. He was also due to travel later to the southern town of Baidoa where the interim parliament sits.

"This is obviously a very serious humanitarian situation in Somalia," he said amid tight security provided by a convoy of white U.N. vehicles and soldiers.

"Those who are already in the camps of the displaced persons are in a bad situation, but the people who fled into the interior are worse than them because we cannot reach them."

Holmes' visit comes a day after Prime Minister Hussein named an "all-inclusive cabinet" and called for talks with Eritrea-based opponents to end an Islamist-led insurgency -- raising hopes that security may be re-established.

Hussein's appointment last month to replace his sacked predecessor was seen by many as an opportunity for reconciliation in Somalia, plunged into chaos when clan warlords toppled dictator Mohamed Siad Barre in 1991.

A contingent of African Union (AU) soldiers has failed to stem the violence from a government-led offensive, supported by the Ethiopian military, to hunt insurgents responsible for almost-daily roadside bombings and grenade attacks.

Holmes said a U.N. peacekeeping mission could only succeed where there is peace to keep.

"What we can do now is plan for a possible mission to Somalia and help the African Union forces in Somalia ... but at the moment it is very hard to even send a fact-finding mission to Mogadishu," he added.