YANGON (Reuters) - The office of Myanmar’s civilian president said on Tuesday that the assassination of a lawyer advising the ruling party on amending a military-drafted constitution was likely an effort to destabilise the country.

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A lone gunman shot Ko Ni, 63, an adviser to the ruling National League for Democracy, in the head in front of onlookers as the widely respected Muslim advocate held his young grandson at Yangon’s international airport on Sunday.

“The initial interrogation indicates the intention to destabilise the state,” the office of President Htin Kyaw said in a statement carried in the state-run Global New Light of Myanmar newspaper. It did not give details.

“Investigations are being carried out by the government to find out the truth. Security has been heightened in the aftermath of the assassination.”

Authorities have detained Ko Ni’s suspected killer, a 53-year-old man. He also shot and killed a taxi driver who tried to apprehend him.

It remains unclear if Ko Ni was targeted for his religion or for his work toward reducing the political role of Myanmar’s military.

But the killing comes at a time of heightened communal and religious tensions in Buddhist-majority Myanmar, where a civilian government led by Nobel laureate Aung San Suu Kyi has been in power for 10 months after a formal transition from decades of military rule.

A heavy-handed security operation in Rakhine state, a region home to many Rohingya Muslims, has led to an estimated 69,000 from the largely stateless community fleeing into neighbouring Bangladesh.

Tens of thousands of people gathered in Yangon on Monday to mourn the death of Ko Ni, who was working on amending the constitution that ruling generals drafted in 2008 and which grants the army a quarter of seats in parliament and control over security ministries.

Suu Kyi did not attend the funeral of her close adviser, and has not issued any statement.

Separately on Tuesday, a commission investigating attacks on border posts in Rakhine State that killed nine police on Oct. 9 and their aftermath has asked for more time due to unspecified “fresh claims” of human rights abuses, state media said.

The commission was to have reported on its findings on Tuesday, including looking into allegations that soldiers committed extrajudicial killings, arbitrary arrests and rape of Rohingya civilians.