BEIJING — Under enormous pressure from China, the Nepalese government restricts the political freedoms of Tibetan refugees living in Nepal, subjects them to abuse and harassment by the security forces, and spies on them for Chinese officials, according to a report released Tuesday by Human Rights Watch.

The 100-page report, “Under China’s Shadow: Mistreatment of Tibetans in Nepal,” documents the repression faced by Tibetans who cross into Nepal, often illegally, from neighboring Tibet, which has been ruled since 1951 by the Chinese Communist Party. The report also discusses how some of those refugees might never enter Nepal proper, saying there are “serious concerns that Nepal may at times forcibly return Tibetans to China.”

Any forced return of Tibetans at the border would be a violation of a “gentleman’s agreement” between Nepal and the Office of the United Nations High Commissioner for Refugees, which runs a transit center for Tibetans in the Katmandu Valley. That agreement is aimed at guaranteeing Tibetans safe passage to India, which has a significant Tibetan refugee population.

Many Tibetans have complained of repression — including torture and suppression of religious practices — under Chinese rule. Those who are caught having tried to enter Nepal or returning to Tibet after a trip to India are often held for weeks or months in detention and interrogated.

Many Tibetans cross through Nepal to India to try to see the Dalai Lama, the spiritual leader of the Tibetans, who lives in the foothills of the Indian Himalayas, or to try to build a better life away from the confines of Tibet and China. There are about 20,000 Tibetans in Nepal.

The flooding of parts of the Tibetan plateau with Chinese security forces since the Tibetan uprising of 2008 and greater cooperation between Chinese and Nepalese forces have resulted in a huge drop in the number of Tibetan refugees arriving in Nepal. In 2013, fewer than 200 refugees were recorded as having fled China to Nepal, compared with an annual average of 2,000 before 2008, Human Rights Watch said.

Nepal was traditionally a haven for Tibetan refugees, but that is no longer the case, given China’s economic influence in the region. Nepal, a poor, landlocked nation, relies on investment from China to help its economy. The government also tries to strengthen ties with China as a counterbalance to India.

In the remote Buddhist kingdom of Mustang, which borders Tibet, China provides $50,000 in annual food aid. Chinese military officials meet there with local Nepalese to talk about what the ceremonial prince of Mustang called “border security” in an interview with The New York Times in 2012. In the 1960s, Mustang was the base for Tibetan guerrillas trained by the C.I.A. to wage war on Chinese troops occupying their homeland.

“The situation for the Tibetan refugee community in Nepal has markedly deteriorated since China’s violent crackdown on protests in Tibet in 2008,” Brad Adams, the Asia director at Human Rights Watch, said in a written statement.

Shankar Prasad Koirala, a spokesman for the Ministry of Home Affairs, said in an interview on Tuesday that Nepal had never mistreated any refugees on Nepalese soil. “Though we have yet to sign international treaties concerning refugees, we are behaving well to all refugees on humanitarian grounds,” he said.

Mr. Koirala said the government would investigate any security officials suspected of mistreating refugees.

In recent years, Tibetans in Katmandu, the Nepalese capital, have complained of detentions by security forces during anti-China protests. Those forces break up rallies and sometimes prevent public gatherings on dates that the Chinese government considers sensitive, such as the Dalai Lama’s birthday. Even celebrations of Tibetan culture can be shut down, refugees say.

Tenzin Chokzin, 22, a Tibetan refugee in Katmandu, said in an interview last month that Tibetans in Nepal were often barred from performing in cultural programs. “Police vigilance has tightened after 2008,” he said. “We are even forced to cancel our cultural programs organized in hotels.”

Mr. Koirala said the Nepalese government could not tolerate any protests that might harm the interests of neighboring countries.

Since 2009, more than 120 Tibetans in Chinese-ruled Tibet have set themselves on fire to protest Communist Party policies. In February 2013, a Tibetan monk in Katmandu, Drupchen Tsering, 25, died after setting himself on fire near a revered Buddhist stupa, or shrine, in Boudhanath, a Tibetan enclave. Tibetans in the area asked for the body, but officials ordered it cremated in the middle of the night, saying no family members had claimed it.

The Human Rights Watch report said China decided to “significantly scale up its economic and political engagement with Nepal” after the 2008 uprising. The culmination of those efforts was a January 2012 visit to Nepal by Wen Jiabao, then the Chinese prime minister.

China has become a top foreign direct investor in Nepal, a move that is, according to the report, “in part aimed at influencing Nepal’s calculations about where its national interests lie.”