The US military's takeover of emergency operations in Haiti has triggered a diplomatic row with countries and aid agencies furious at having flights redirected.

Brazil and France lodged an official ­protest with Washington after US military aircraft were given priority at Port-au-Prince's congested airport, forcing many non-US flights to divert to the Dominican Republic.

Brasilia warned it would not ­relinquish command of UN forces in Haiti, and Paris complained the airport had become a US "annexe", exposing a brewing power struggle amid the global relief effort. The Red Cross and Médecins Sans Frontières also complained about diverted flights.

The row prompted Haiti's president, René Préval, to call for calm. "This is an extremely difficult situation," he told AP. "We must keep our cool to co-ordinate and not throw accusations at each other."

The squabbling came amid signs that aid was reaching some of the hundreds of thousands of people in desperate need of water, food and medicine six days after a magnitude 7 earthquake levelled the capital, killing more than 100,000, according to Haitian authorities.

The UN was feeding 40,000 and hoped to increase that to 1 million within a fortnight, said the secretary general, Ban Ki-moon, as he arrived in Port-au-Prince yesterday. "I am here with a message of hope that help is on the way," he said, speaking outside the severely damaged national palace. He also acknowledged "that many people are frustrated and they are losing their patience."

Ban said he has three priorities in Haiti: saving as many lives as possible, stepping up humanitarian assistance and ensuring the co-ordination of aid coming into the country. "We should not waste even a single item, a dollar," he said.

The plight of 80 elderly people at a partially collapsed municipal hospice just a mile from the airport, now a huge aid hub, showed the desperate need. The body of a dead 70-year-old man rotted on a mattress, nearly indistinguishable from the exhausted, hungry and thirsty people around him. "Others won't live until tonight," an administrator, Jean Emmanuel, told the Associated Press.

The Haitian government has established 14 food distribution points and aid groups have opened five emergency health centres. Water-purification units – a priority to avert disease and dehydration – were arriving.

But with aftershocks jolting the ruins, bloated bodies in the street and severe shortages of water and food many survivors had had enough: an exodus trekked on foot out of the city to rural areas.

The security situation worsened, with some looters fighting with rocks and clubs for rice, clothing and other goods scavenged from debris. In places the embryonic aid machine did not even try to organise distribution. Aid workers tossed out food packets to crowds and US helicopters took off as soon as they offloaded supplies, prompting scrambles in which the fittest and strongest prevailed.

"They are not identifying the people who need the water. The sick and the old have no chance," Estime Pierre Deny, ­hoping to fill a plastic container with water amid a scrum of people, told Reuters.

Frustration over aid bottlenecks among donors became tinged by national rivalry as it became clear the US was taking ownership of the crisis. A vanguard of more than 1,000 US troops was on the ground and 12,000 were expected in the region by today, including marines aboard the aircraft carrier USS Carl Vinson which anchored offshore as a "floating airport".

The Haitian government, paralysed by the destruction of the presidential palace and ministries, signed a memorandum of understanding formally transferring control of Toussaint L'Ouverture airport to the US. Former president Bill Clinton said he will travel to Haiti today to meet with government officials and deliver much-needed emergency supplies.

The UN mission, which had a 9,000-strong peacekeeping force in Haiti before the quake, seemed too stunned by its own losses to take control. Its dead include its Tunisian head, Hédi Annabi, his Brazilian deputy, Luiz Carlos da Costa, and the acting police commissioner, Doug Coates, a Canadian.

Flights seeking permission to land continuously circle the airport, which is damaged and has only a single runway, rankling several governments and aid agencies. "There are 200 flights going in and out every day, which is an incredible amount for a country like Haiti," Jarry Emmanuel, air logistics officer for the UN's World Food Programme, told the New York Times. "But most flights are for the US military. Their priorities are to secure the country. Ours are to feed. We have got to get those priorities in sync."

France, which as the former ­colonial power expects a prominent role, ­protested when an emergency field hospital was turned back. The foreign minister, Bernard Kouchner, said the airport was not for the international community but "an annexe of Washington", according to France's ambassador to Haiti, Didier Le Bret.

Brazil, which saw its leadership of the UN peacekeeping mission as a calling card of its burgeoning influence, was also indignant when three flights were not allowed to land. The foreign ministry reportedly asked Hillary Clinton to grant Brazil priority over chartered flights. Nelson Jobim, the defence minister, said Brazil would not relinquish command duties and suggested it, not Washington, would continue to lead UN forces. Analysts said it was vital command issues be resolved.

The Red Cross and Médecins Sans Frontières complained about flights with medical staff and equipment which were redirected to the Dominican Republic. "We are all going crazy," said Nan Buzard, of the American Red Cross.

The Obama administration has enlisted former presidents George Bush and Bill Clinton to spearhead relief efforts. In a series of interviews both men deflected right-wing accusations that the White House was seeking political advantage from the disaster. "I'd say now is not the time to focus on politics," Bush said, as he sat beside his predecessor. "You've got children who've lost parents. People wondering where they're going to be able to drink water."