The UN Secretary-General, Kofi Annan, has urged the Security Council to heal the "deep divisions" caused by the Iraq crisis and reassert itself by tackling the country's humanitarian needs.
Some aid is now reaching Iraqis in the south
Addressing an emergency meeting of the Security Council, Mr Annan called for a mandate to supply aid to the Iraqi people, whatever the outcome of the war.
He said the responsibility for getting aid through safely lay with the belligerents, but international organisations would do all they could to help.
"We are living through a moment of deep divisions which, if not healed, can have grave consequences for the international system and relations between states," he warned.
The emergency session - scheduled to resume at 1430 GMT on Thursday - was called at the request of the Arab League and the Non-Aligned Movement.
Mr Annan said he hoped the council members would overcome their differences over reactivating the oil-for-food programme in Iraq, which was suspended last week following the withdrawal of all international UN staff.
UN officials quoted by Reuters news agency say the UN is preparing its biggest ever appeal for emergency humanitarian aid, pushing for more than $2bn for war-torn Iraq.
The Iraqi Ambassador, Mohammed al-Douri, used the meeting to denounce the invasion of his country.
He accused the US and Britain of defying the will of the international community and of launching "colonial, Anglo-Saxon aggression" against Iraq.
Mr Annan told the session that the belligerents in Iraq had the "primary responsibility" for meeting the country's humanitarian needs.
"But the humanitarian agencies of the United Nations are ready to help," he said.
The first convoys of aid - donated by Kuwait - are finally beginning to arrive in Iraq nearly a week after the invasion.
Basra is facing a severe shortage of safe drinking water, while Iraqis in the port of Umm Qasr say they have been without food for five days.
Mr Annan said that, while many asked why Iraq had not taken the chance to disarm peacefully, many people around the world also questioned whether the military action was legitimate.
The Arab League, many EU members and other countries have criticised the invasion, but no draft resolution on the war has been proposed yet at the Security Council.
"We call upon you to put an end to this war and to call for the immediate withdrawal of invading forces," said the Arab League's representative to the UN, Yahya Mahmassani.
"The credibility of the Council, the credibility of the whole international system, is collapsing under the bombing of Basra and
Baghdad," he warned.
Any resolution opposing the war would almost certainly be vetoed by the UK and US, the BBC's Susannah Price reports from the UN.