A Burmese court has added 10 years to the prison sentence of a young news photographer who was arrested after taking pictures at the scene of a bomb attack last year.

The court sentenced 21-year-old Sithu Zeya on Wednesday under Burma's harsh Electronics Act, saying he had circulated material that could damage tranquillity and unity in the government.

Sithu Zeya was already serving an eight-year term on immigration and illegal associations charges. Prosecutors said he had admitted to associating with an exiled media group, the Democratic Voice of Burma, and receiving media training in Thailand.

When arrested, Sithu Zeya had been taking pictures at the scene of bomb blast that killed 10 people and wounded 170 during a traditional New Year's water festival in April 2010 in Rangoon.

The media watchdog group Reporters Without Borders denounced the extended sentence, saying Sithu Zeya has committed no crime.

The group said the case shows that moves by the new Burmese government to engage with its critics are just a public relations strategy and do not indicate any real intention to give its citizens more freedom.

U.S. special envoy Derek Mitchell ended a five-day visit to Burma earlier Wednesday. He said its leaders had expressed their commitment to democratic reform. Mitchell said he pressed them to back up their words with actions.

U.S. Assistant Secretary of State Kurt Campbell is expected to meet Burmese Foreign Minister Wunna Maung Lwin on the sidelines of the U.N. General Assembly meeting in New York next week to assess Burma's commitment to real reform.