US troops are fanning out across Haiti as aid operations gather momentum, a week after the devastating earthquake.UN officials said aid distribution points were being set up in the capital and UN security forces would accompany US troops as they delivered supplies.
Helicopters dropped scores of US troops in the presidential palace grounds, who then moved to secure a nearby hospital.
Meanwhile, the UN Security Council has voted to boost its peacekeeping forces to help control outbursts of looting.
Anger has been growing in the streets of the capital, Port-au-Prince, as people wait for help.
The US military has begun delivering food and water to distribution points in the capital and elsewhere by helicopter, after congestion at the airport delayed deliveries of aid.
Some 14,000 ready-to-eat meals and 15,000 litres of water were dropped north-east of Port-au-Prince on Monday, the US said.
Meanwhile, the UN approved a recommendation by Secretary General Ban Ki-moon to boost UN troop numbers in Haiti by 2,000 for six months, and UN police numbers by 1,500.
Mr Ban said he was grateful to the UN Security Council for its swift action, calling it "a clear signal that the world is with Haiti".
He said the UN was in discussion with member states, and he hoped to have the extra troops and police to deploy soon. The UN mission in Haiti currently numbers about 9,000.
There have been reports of widespread violence and looting.
But the UN has played down worries over security, saying that despite violent incidents, the overall situation is calm.
US Army Maj Gen Daniel Allyn, deputy commander of the Joint Task Force on ongoing relief efforts, echoed that message, saying the security situation was "relatively calm" and that aid distribution points were orderly.
He said there were "pockets of instability", but that UN forces and the Haitian national police were addressing security needs with "agility".
There were more than 2,000 personnel on the ground and 5,000 afloat, he said, adding that 10,000 troops in total would be arriving in the coming weeks, half of whom would be directly involved in distributing humanitarian aid.
Mr Ban said the UN's goal was to increase the number of people receiving food to 1 million this week and at least 2 million in the following two weeks.
Addressing concern that aid has been too slow to reach desperate Haitians, Mr Ban said the situation on the ground was "overwhelming" but that UN efforts were "gearing up quickly".
"For those who have lost everything, of course, help cannot come soon enough," Mr Ban said. "But we are working day and night."
'Test of resolve'
Last week, US Defence Secretary Robert Gates said airdrops had been ruled out because they might do more harm than good.
Mr Gates warned that they could trigger riots if there was no proper structure on the ground to distribute supplies.
But the BBC's Nick Davis in Port-au-Prince says that the US military is now securing areas on the ground before pallets of food and water are parachuted in.
British Prime Minister Gordon Brown said on Tuesday that Haiti remained a major test for the international community.
"It is a test of our compassion. It is a test of our resolve. And it is also a test of our ability to co-ordinate our actions together."
France's co-operation minister, Alain Joyandet, had suggested on Monday that the US was "occupying" Haiti and urged the UN to "clarify" the US role.
However, a statement from President Nicolas Sarkozy on Tuesday said France was "very satisfied" with the co-operation and praised the US for its "exceptional mobilisation".
The UN says dozens of search and rescue teams are now on the ground.
On Tuesday, UN spokeswoman Elisabeth Byrs said 90 people had been pulled out alive since the earthquake and rescue efforts were now concentrated outside the capital.
She insisted there was still hope for survivors. "The climate is mild, there are significant air pockets. The problem is dehydration but for the moment there is still a chance," she said.
At least 70,000 people who died in the earthquake have already been buried.
On Tuesday, the Paris Club of creditor governments, including the US, UK, France and Germany, called on other nations to follow its lead in cancelling debts to Haiti. Venezuela and Taiwan are the biggest other creditors.
Meanwhile, the bodies of eight Chinese nationals killed in the quake have arrived back in Beijing in a high-profile ceremony attended by relatives and top officials.
