KATHMANDU, Nepal — A helicopter on a relief mission for the international aid agency Doctors Without Borders crashed in a district northeast of Kathmandu on Tuesday afternoon, killing four people on board.

Relief and rescue operations in Nepal since the devastating earthquake on April 25 have been treacherous, with dangers compounded by difficult terrain, hard-to-reach villages nestled into remote hillsides and inclement weather.

Most of the villages affected by the earthquake are scattered along these hillsides, and foreign aid organizations, the Nepali government, with the help of foreign governments, have been working to provide much-needed relief.

In May, a United States Marine helicopter, a UH-1 Huey, crashed on a high mountain pass near the village of Charikot while on a relief operation, killing six Marines on board and two Nepalese soldiers.

The helicopter that crashed in the Sindhupalchowk district on Tuesday was run by the private company Mountain Helicopter Pvt. Ltd., and was bringing three doctors from Doctors Without Borders back to Kathmandu, according to a Nepal police spokesman, Kamal Singh Bam. The pilot, Subek Shrestha, was killed, he said, and a total of four bodies had been found at the crash site.

Laxmi Prasad Dhakal, a spokesman for Nepal’s Home Ministry, confirmed that four people were on board, and that there were no survivors.

Though Mr. Dhakal said that the government had not identified the reason for the crash, Krishna Prasad Gyawali, the chief district officer in Sindhupalchowk, said that the helicopter had been flying at a low altitude in the middle of a dense forest when it hit a high-tension electrical wire.

Another rescue helicopter was sent to the site of the crash on Tuesday.

“There is a fire at the crash site,” Mr. Gyawali said. “The scene is horrible.”

Rasmus Baastrup, a press officer for Doctors Without Borders currently in Nepal, wrote in an email that the helicopter was chartered by the organization to deliver humanitarian aid. Doctors Without Borders is working on confirming the identities of the victims in the crash, he wrote.

Several private helicopters have been employed for search, rescue and relief operations since the magnitude 7.8 earthquake in Nepal on April 25, and a magnitude earthquake 7.3 there in May killed nearly 8,700 people.