If we deliver to the Afghan people what we promised, this will be a great day - if we don't deliver, this will go into oblivion

Hamid Karzai

"The number one priority is to maintain and further provide peace and stability for Afghanistan, to give the Afghan people an opportunity to live at absolute ease," said Mr Karzai.

He was speaking to journalists after being sworn in as head of a 30-strong United Nations-backed government at an emotional ceremony in the capital, Kabul.

"We basically need billions of dollars to overcome the difficulties in all spheres of economic activity and the infrastructure.

Hamid Karzai is promising to work for peace

"The revival of certain industries, the revival of agriculture, schools and hospitals... there is really no area in which Afghanistan does not require assistance," he said.

Several countries have already pledged aid to Afghanistan, whose economy is in ruins after more than 20 years of war and tribal division.

The inauguration of the interim government, which will serve for six months, was attended by 2,000 tribal leaders, incoming cabinet members and foreign diplomats.

Click here for a who's who of the Afghan powerbrokers

Security was tight, with armed soldiers and police patrolling in the grounds of the interior ministry, accompanied by a small contingent of Royal Marines who are the vanguard for the British-led international security force.

"The significance of this day in Afghan history will really depend on what happens in the future," Mr Karzai told a news conference in the presidential palace.

"If we deliver to the Afghan people what we promised, this will be a great day. If we don't deliver, this will go into oblivion."

A picture of the late Ahmed Shah Masood dominated the ceremony

The BBC's Ian McWilliam in Kabul says the greatest danger for Afghanistan now is a return to factional fighting.

Jobs in the new government have been divided among Afghanistan's ethnic groups. But some Pashtun leaders are angry because a majority of posts have gone to the Tajik-dominated Northern Alliance.

But our correspondent says it is significant that the two most powerful regional warlords - Abdul Rashid Dostum from the northern city of Mazar-e-Sharif and Ismail Khan from Herat in the west - were present at Mr Karzai's inauguration.

The new prime minister described both men as fine Afghans and said he had excellent relations with both.

Mr Karzai also reiterated his commitment to capturing and trying leaders of the former Taleban regime, which was toppled by US military action in the wake of the 11 September terror attacks on New York and Washington.

"They will be taken to court and our people will be given justice," he said.

Mr Karzai said Afghanistan must come to terms with its past - and that a war crimes commission was "not a bad idea".

He promised his administration's full co-operation with US efforts to track down al-Qaeda fighters who were still in Afghanistan and to arrest its leader, Osama Bin Laden.

The way ahead

Mr Karzai, a 44-year-old Pashtun leader, was selected to head the interim cabinet at a UN-sponsored meeting of Afghans in the German city of Bonn.

During the next six months, his cabinet is expected to organise a loya jirga, or grand council, that will choose a government to rule for two years while preparing for elections.

Lakhdar Brahimi, the UN representative who brokered the new government's make-up at the Bonn talks, said Afghanistan had suffered for too long.

"Each and every Afghan has been touched by this tragedy and has grown tired of war. People have now put their faith in this interim administration, and this faith must be rewarded," he said.

The ceremony, attended by representatives from every province in the country, marked the end of a "long dark night of conflict and strife".

Mr Brahimi added: "This agreement, although far from perfect, has been warmly welcomed by the people of Afghanistan and by all the countries of the world."