A leading medical relief group says it is withdrawing from Thailand after 35 years in the country because of continuing disagreements with the government.

Médecins Sans Frontières issued a statement Thursday saying it had failed to secure permission to provide health care to undocumented migrants and vulnerable populations, despite months of negotiations and discussions.

MSF says it was forced to close its projects in Samut Sakhon and three Pagodas Pass, depriving 55,000 people of their only access to basic health care services.

It says an estimated 1.5-2 million migrants are still undocumented. Despite closing down its permanent project in Thailand, MSF vows to remain “alert and ready” to respond to emergencies as needed.

The humanitarian group says its mission in Thailand began in 1976, when it provided assistance to Cambodian refugees fleeing the Khmer Rouge regime. Over the years, it provided support for refugees from Burma, and helped Thailand become one of the first countries to introduce free antiretroviral treatment for people living with HIV/AIDS.