All four KFC and Pizza Hut restaurants in Nepal shut down on Tuesday saying that staff had attacked and threatened to kill branch managers.

Devyani International, which operates outlets of KFC and Pizza Hut in Nepal and neighbouring India, wrote a letter to authorities announcing the immediate closure of its eateries in the capital Kathmandu.

"In order to disrupt our operations, some staff have physically attacked and threatened to kill the senior managers," the company said in a letter leaked to local media and seen by AFP.

"These acts have put the life of senior managers at risk. To maintain the safety of our restaurants and the staff, we have shut down our services for an indefinite period," it said.

The shutters were down at the four restaurants on Tuesday, and Devyani International and the police were unavailable for comment.

KFC and Pizza Hut, Nepal's only international fast-food chains, opened their first branches in the country three years ago, generating long queues of locals wanting to sample international cuisine.

Their arrival was seen as a sign of an improving environment for foreign firms in a country ravaged by bloody civil war between 1996 and 2006, when a peace deal was reached between Maoists and the government.

During the violence, rebels targeted foreign ventures including Coke, Pepsi and Unilever, but more recently Kathmandu has seen rapid growth in restaurants, malls and supermarkets selling foreign goods.