A team of 49 U.S. military experts is visiting Nepal to train the army to help fight Maoist rebels and to teach them how to operate weapons recently acquired from Washington.
The United States supplied the Nepalese army with about 3,000 M-16 rifles earlier this month.
The Nepalese army was deployed to crush the rebellion a year-and-a-half ago after the Maoists broke a ceasefire and walked out of peace talks.
But the Nepalese government says troops are in urgent need of modern equipment to fight the rebels, and has been appealing to Western governments for assistance.
Several countries have responded, after expressing concern at the upsurge in violence in the mountain kingdom.
The U.S. has approved $12 million in military aid to Nepal. It has also warned the rebels that it could include them on a list of terror groups.
Britain has promised to provide aid and equipment to the Nepalese government. India has supplied helicopters and night vision equipment, and promised more support to the government to end the rebellion.
Robert Boggs, deputy head of the U.S. embassy in Kathmandu, told the AFP news agency that the U.S. military experts will stay in the country for a few weeks. He strongly denied reports in the local media that the the U.S. team would launch a joint operation with the Nepalese army against Maoist rebels.
Maoist rebels are fighting to end the constitutional monarchy and establish a communist republic in the mountain kingdom. More than 7,000 people have been killed in the rebellion. Human rights groups say nearly half of those killed are civilians, the army says most of them are rebels.