YANGON, Myanmar — A day after a prominent human rights lawyer was fatally shot in Yangon, Myanmar’s government said on Monday that the gunman had been trying to undermine stability in the country.

The lawyer, U Ko Ni, 65, an adviser to Myanmar’s leader, Daw Aung San Suu Kyi, was shot in the head at close range as he was leaving Yangon International Airport on Sunday. The police arrested a suspect, identified as U Kyi Lin, and seized two handguns.

“According to an earlier interrogation, the motivation of the incident is to undermine the country’s stability,” the president’s office said in a statement.

Mr. Ko Ni, a Muslim and a member of the governing National League for Democracy, was returning from Indonesia with other government officials and civic leaders who had traveled there to discuss democracy and conflict resolution. He wrote six books on human rights issues and democratic elections, and he was actively involved in the interfaith peace movement.