Officials said the British aircraft larger than the MI-17 would face hurdles flying in Nepal’s difficult terrain. Some national security concerns are also responsible for the halt, said a government official. The country’s only international airport is overcrowded with planes from India, China and the United States.

“As far as I know, the government has not given clearance to the British aircraft to fly to Kathmandu,” said Nepal Army spokesman Jagadish Chandra Pokhrel.

A British Embassy statement said three Chinook helicopters would be made operational in Kathmandu as part of the UK’s relief effort. “These advanced helicopters are able to carry vital relief supplies to isolated high altitude areas across the country which are currently challenging to access.”