YANGON (Reuters) - Three Myanmar reporters detained at an undisclosed location by the army will be charged under a colonial-era statute against “unlawful association” and face up to three years in jail, government and army officials said on Tuesday.

The military arrested the journalists in Myanmar’s northeastern Shan state on Monday after they covered a drug-burning event organized by the Ta’ang National Liberation Army (TNLA), an ethnic armed group designated as an “unlawful association” by the Yangon authorities.

The reporters are from two media outlets publishing both in Burmese and English, the Democratic Voice of Burma (DVB) and the Irrawaddy. They were among the few media organizations providing the world independent coverage of Myanmar when it was under military rule before a democratic transition began in 2011.

The arrests alarmed Myanmar’s media community, fuelling fears that freedom of speech has become increasingly restricted since the government of Nobel Peace Prize winner Aung San Suu Kyi took power in April last year.

“Everyone should be treated according to the law,” Suu Kyi’s spokesman, Zaw Htay, told Reuters. He added that the military told him it planned to charge the reporters under the Unlawful Association Act. A military source confirmed this.

Citing information from the army, Zaw Htay said the three reporters and four other men arrested with them were “being treated very well” at a military guesthouse and would be handed over to the police “tomorrow or the day after tomorrow”.

Despite pressure from human rights bodies and the West, Suu Kyi’s government has retained loosely worded security laws dating to British colonial rule, which ended in 1948, and decried by monitors as violating free speech.

Suu Kyi has not spoken out against increasingly frequent arrests of reporters and activists.

The Unlawful Association Act has long been used by the authorities to arbitrarily arrest and detain people in Myanmar, in particular people in ethnic and religious minority areas, according to human rights watchdog Amnesty International, which has called on the government to release the journalists.

Western governments have also expressed their concern over the incident.

The U.S. State Department said it was “deeply concerned” about arrests of Thein Zaw from The Irrawaddy, and Aye Nai and Pyae Phone Naing from DVB, particularly in light of other recent arrests of journalists.

“We urge immediate action on this matter consistent with international standards of human rights and freedom of the press,” a spokeswoman, Katina Adams, said.

“A free press is vital to the success of peace and national reconciliation process,” she said.

The editors from the publications where the reporters work told Reuters they had tried obtaining explanations from the military and the government, but to no avail.

“We are all concerned about the situation, because we have lost connection with the detainees,” Than Win Htut, a DVB editor, told Reuters. “Their families have the right to know what happened to them.”