YANGON (Reuters) - Anti-war protesters in Myanmar on Wednesday urged government leader Aung San Suu Kyi to take action against police who this month broke up a peace rally and arrested them, and raised new concern about freedom of speech.

Myanmar's State Counsellor Aung San Suu Kyi enters a limousine after she meets Vietnam's Prime Minister Nguyen Xuan Phuc (not pictured) in Hanoi, Vietnam April 19, 2018. REUTERS/Kham

Riot police in the main city of Yangon used batons on May 12 to break up a rally called to show support for victims of fighting in northern Myanmar, arresting 17 organizers for disturbing the public and holding a protest without permission.

The scuffles between baton-wielding police and protesters have sparked an outcry among activists and lawmakers over what they see as risks to free expression under the government of Nobel Peace Prize laureate Suu Kyi.

In a letter sent to top government officials including Suu Kyi and President Win Myint, eight of the rally organizers said action should be taken against the police, which come under the control of Myanmar’s powerful military.

“Police came, arrested us and beat us for no reason, and that’s why we are demanding action to be taken against police who violently handled the peaceful protest,” the eight organizers said in their letter.

“The lawless action by the authorities should be investigated for our loss of citizens’ rights,” they said.

Government spokesman Zaw Htay was not immediately available for comment. Police spokesman Myo Thu Soe said he was not aware of the letter and declined to comment.

A movement of mostly young anti-war activists has in recent months spread to various parts of the country, exposing frustration with Suu Kyi’s struggle to fulfil a promise to end decades of war by autonomy-seeking ethnic minority guerrillas.

The military, which ruled the country for decades, oversees internal security even though a civilian-led government has been in power since 2016, after Suu Kyi’s party swept an election.

More than 6,000 people have fled their homes in recent weeks since the army launched a new offensive against the Kachin Independence Army insurgent group in Myanmar’s north.

Fighting has also intensified in other ethnic minority areas.

A freedom of speech monitoring group, Athan, has said more than 42 activists across the country have been charged in May for participating in rallies protesting against the conflict.

The 17 organizers of the May 12 rally, who were detained but later released, face a month in prison and fines.

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