* Death toll in remote Afghan village could total 2,700
* Second slide hit locals trying to help those hit by first
* Some survivors sleeping outside in freezing cold (Adds Obama-Karzai phone call in paragraph 8)
By Mirwais Harooni
AAB BAREEK, Afghanistan, May 4 (Reuters) - Six-year-old Abdul Maqsood stood outside his neighbour's simple mud-brick home, staring aghast at the damage caused by a landslide which had slammed into his village in remote northeast Afghanistan. Then the rumbling started.
Maqsood had no idea that the entire side of the bare mountain above him, drenched by a week of heavy rain, had fractured and was about to cave in.
The second, even bigger landslide happened so quickly that Maqsood had no time to run. He was swamped by a wall of mud that swallowed up his home and some 300 others around him, taking hundreds, possibly thousands of lives in Afghanistan's worst natural disaster in a decade.
"It sounded like a bomb and I screamed, called my father and mother for help," he told Reuters on Sunday from a makeshift clinic in a tent where the injured were being treated by local and Red Cross medics.
"It was so dark and dusty everywhere and I didn't know what happened," said Maqsood, his head and leg wrapped in bandages.
The boy's father, a shovel already in hand after helping victims from the first landslide, rushed to back to find his son. Twenty minutes later, he dragged Maqsood from the earth and debris.
In one the poorest areas of Afghanistan - where most people do not have electricity and roads are almost non-existent - Maqsood's family was lucky: his mother and brother were also saved.
The United Nations on Sunday put the death toll from Friday's massive landslide in Badakhshan province, bordering Tajikistan, at up to 500. Local officials say the number killed could be as high as 2,700.
U.S. President Barack Obama called Afghan President Hamid Karzai on Sunday to express his condolences and offer additional assistance, the White House said in a statement.
It is unlikely the final figure will ever be known, as officials say it is impossible to retrieve the bodies buried in up to 50 metres (160 feet) of mud and debris.
"We cannot continue the search and rescue operation anymore, as the houses are under metres of mud," said Gul Mohammad Bedaar, deputy governor of Badakhshan province. "We will offer prayers for the victims and make the area a mass grave."
Fears of another landslide prompted officials to evacuate the remaining 700 families, or about 4,000 people, to safer ground nearby. They may never return to live in their homes in Aab Bareek.
Afghan army helicopters delivered water, food, medicine and tents on Sunday, while aid agencies and local relief workers slowly arrived after a difficult journey over a pot-holed road.
The U.N. agency in charge of relief operations, the Office for the coordination of Humanitarian Affairs (OCHA), said the displaced were largely being accommodated with host families, with some in tents.
But villagers expressed their anger with the relief effort, saying that many had already spent two nights in the open in near-freezing conditions.
"At least they should give us a shelter to live in," said Bibi Nawroz, who said she had lost eight members of her family in the disaster.
Local officials echoed their concerns, calling on the government and foreign aid agencies to act more quickly.
"There are thousands of families who are in desperate need of help and hundreds of other homes are at risk, or possibly another landslide," said deputy governor Bedaar.
"The government and relief organisations must act swiftly and send us more aid and equipment. What we have so far is not enough."
Over the past fortnight, about a third of the country has been flooded due to heavy seasonal rains and snow melt, killing 159 people.
The United Nations says 71,000 have been affected in a country prone to natural disasters due to its geographical location and years of environmental degradation.
Despite offers of help from the United States and NATO-led coalition troops battling Taliban insurgents, the Afghan government says it can manage on its own, with the assistance of aid agencies.
Relations between Kabul and Washington are at an all-time low over Karzai's refusal to sign a security agreement allowing a small U.S. force to remain in the country at the end of the year.
Twelve years after U.S.-led forces invaded Afghanistan to drive the Taliban from power, foreign combat troops will withdraw on Dec. 31, leaving security in Afghan hands.
The United States wants to keep a force of less than 10,000 troops there for counter-insurgency and training purposes. (Additional reporting by Hamid Shalizi; Writing by Jeremy Laurence; Editing by Robin Pomeroy and Eric Walsh)