Nepal's government today said it has denied entry to three British military helicopters sent to help the earthquake relief effort because of fears they could damage buildings when landing.
A foreign ministry spokesman said the Chinook helicopters, which arrived in New Delhi last week en route to the quake-hit country, were too big to land.
"We have told the British authorities that they cannot fly their Chinook helicopters here because our technical team says they are likely to damage the houses and other buildings in the Kathmandu valley," spokesman Tara Pokharel told AFP.
"We are worried about broken windows and roofs being blown off by these big helicopters."
The April 25 earthquake killed more than 8,000 people and left thousands more homeless and in desperate need of food, clean water and shelter.
Getting relief to the worst-hit villages is a huge challenge because many are in remote mountainous terrain that is only accessible by helicopter or on foot.
India, China and the US have sent helicopters and are helping take food, water and tents to affected communities.
But there has been criticism of the US decision to send large Osprey helicopters, which experts say are ill-suited to Nepal's mountainous terrain.
Local media reported that the down-draft from an Osprey relief flight blew the roof off a small building in a quake-hit village as it delivered aid.
A US embassy official told AFP that such accidents were rare.
"We are looking into whether the damage to the roof was caused by the Osprey or the quake... Obviously such incidents are rare and if it turns out to be true, we will take care of the damage," the official said.
So far the Ospreys have delivered 21.5 tonnes of aid, he said.
Steven Bruce Bokan, chief flying instructor for Nepalese helicopter company Manang Air, said the British Chinooks and US Ospreys were "basically useless" in the Himalayas.
"They may work in deserts and other places which have huge areas for landing and take-off, but they are too big to land in the Himalayas," Bokan told AFP.
