A gunman has killed a legal adviser for Myanmar's ruling National League for Democracy, shooting the lawyer in the head at close range as he walked out of the Yangon airport, the Government says.

Key points: Ko Ni was arriving back in Myanmar when he was shot at close range

Ko Ni was arriving back in Myanmar when he was shot at close range The victim is a Muslim and a critic of his party for ignoring Muslims in the general election

The victim is a Muslim and a critic of his party for ignoring Muslims in the general election Amnesty International says the killing has hallmarks of a political assassination

The gunman was arrested after he killed Ko Ni, a prominent member of Myanmar's Muslim minority, the Ministry of Information said in a video posted on state-run MRTV.

Ko Ni was the Supreme Court advocate for the NLD and a longstanding legal adviser to the country's leader Aung San Suu Kyi. He had just arrived from a trip overseas.

A friend of Ko Ni who witnessed the shooting said the suspected assassin also shot a taxi driver who tried to stop him from fleeing.

"As I stopped my car by the airport, that's where I saw Ko Ni's body lying on the walkway outside of the airport and I couldn't believe that just happened," said Thet Paing Soe, a friend and an NLD supporter.

"Then as the shooter tried to run away, the police arrested him."

The Ministry of Information identified the suspect as Kyi Linn from Mandalay. The motive was not known.

Kyee Myint, a former chairman of the Myanmar Lawyer Network who has a close relationship with Ko Ni, also confirmed his death.

"It is a big loss for us that Ko Ni, our beloved friend, has been killed," he said.

"He is the face of the democracy in our country and this is a big loss for us."

Calls to Ms Suu Kyi's office were not answered, and other leaders of the NLD were not reachable.

Ko Ni was one of the country's most prominent Burmese Muslims. He criticised the NLD in 2015 for not putting up Muslim candidates in the general election.

Myanmar is a mainly Buddhist country and anti-Muslim sentiments have increased in recent years following deadly communal violence concentrated in the western state of Rakhine that is home to many Rohingya Muslims.

Amnesty International urged an independent investigation and said the killing of Ko Ni had the hallmarks of a political assassination.

"His death will send shockwaves across the human rights community in the country and beyond, and the authorities must send a clear message that such violence will not be tolerated and will not go unpunished," said a statement from Josef Benedict, Amnesty's regional deputy campaigns director.

The group called Ko Ni a tireless human rights campaigner and expressed condolences to his family.

AP