An ethnic rebel leader was sentenced to 20 years in prison for high treason Tuesday in Myanmar, whose new government is trying to reach a cease-fire agreement with the Karen and other longfractious ethnic groups.

The court in northern Yangon also gave Mahn Nyein Maung a three-year sentence for unlawful association, to be served concurrently, his lawyer Aung Thein said.

He is a central executive committee member of the Karen National Union, which has been seeking greater autonomy for more than half a century and has carried out an armed struggle for most of that time.

The military-backed but elected government began seeking cease-fires with ethnic rebel groups as part of political reforms started last year after decades of repression under military rule.

While the central government has been holding talks with the KNU, the group remains an illegal organization.

In January, President Thein Sein's government released hundreds of political prisoners under an amnesty to foster political reconciliation, but the KNU has said at least 60 of its members remain behind bars.

Aung Thein said the action against a Karen leader such as Mahn Nyein Maung "is inappropriate at a time when the government is vigorously engaged in peace talks with ethnic nationality groups."

Because the government has reached a tentative ceasefire agreement with the Karen National Union, the sentencing of a Karen leader could create misunderstanding and will not be helpful toward the government's "national reconciliation efforts with ethnic groups," he said.

The government and the Karen rebels are supposed to have further talks next month.

Mahn Nyein Maung is famous for his escape from a detention camp on Coco Island in the Andaman Sea, an adventure about which he afterward wrote a book.

He had been jailed in 1960 on political charges, but 10 years later, along with two other political prisoners, slipped away and made his way to the mainland on a makeshift raft -- only to be recaptured.

Mahn Nyein Maung was arrested last year by Chinese immigration officials and was sent to Thailand, where the KNU maintains offices. However, Thailand refused him entry and sent him back to China, which refused to allow him entry and deported him to Myanmar. He then served a six-month jail term for immigration violations, including carrying a fake passport, before being tried for treason.

The sentence for high treason was life imprisonment, which is treated as 20 years.