YANGON, March 13 (Reuters) - A Myanmar court sentenced a top leader of an ethnic rebel group to life imprisonment for high treason on Tuesday, his lawyer said, a move that could complicate a government-led peace process aimed at settling decades-old separatist conflicts.
Phado Man Nyein Maung, a senior political figure in the Karen National Union (KNU), was found guilty under Myanmar's Illegal Association Act for his involvement in a long-running rebellion and is expected to serve 20 years in prison.
His lawyer, Kyi Myint, told Reuters he had sought leniency because his client had been liaising with the government on a possible truce with the KNU while awaiting trial in Yangon's notorious Insein Prison since July 2011. He was deported from China.
"During interrogation, responsible government officials asked him for advice on peace talks with the KNU and they also assured him that they would request clemency from the president," he said.
"I did my best to convince the authorities to free him taking into account his role in the peace talks with the KNU, but it was in vain."
The jailing of Phado Man Nyein Maung, 70, could create another hurdle for the new civilian government in its drive towards "everlasting peace" after decades of on-off fighting in the ethnically diverse, resource-rich country.
Western countries have made a successful peace process with separatist groups in Myanmar one of their main demands for lifting sanctions.
The KNU has fought for secession from the state since Myanmar was granted independence from Britain in 1948.
The group and its military wing, the Karen National Liberation Army (KNLA) agreed a ceasefire with government negotiators on Jan. 12, but mistrust between both sides remains high after 62 years of fighting and allegations of widespread atrocities by Burmese troops against Karen civilians.
Peace talks had been held on six previous occasions since 1949, but no lasting agreement was reached. Political talks on the path towards a long-term settlement with the KNU were expected to start within the next two months.
Preliminary ceasefires have been agreed with 12 of the 16 armed ethnic groups or political organisations that have responded to President Thein Sein's appeal last August for all sides to start dialogue.
Phado Man Nyein Maung has been jailed at least two occasions before alongside hundreds of other prominent politicians and student leaders under former military regimes. The new government has released more than 600 political prisoners since last May.
He spent time in jail on the Coco Islands in the Indian Ocean mid-1960s but escaped, only to be re-arrested soon after. (Reporting by Aung Hla Tun; Writing by Martin Petty; Editing by Daniel Magnowski)