The tunnels are said to be large enough to accommodate heavy vehicles
Two Burmese officials have been sentenced to death for leaking details of secret government visits to North Korea and Russia, the BBC has learned.
The officials were also found guilty of leaking information about military tunnels allegedly built in Burma by North Korea, a source in Burma said.
A third person was jailed for 15 years, the source added.
The military rulers in Burma (Myanmar) have so far made no public comments on the case.
The source told BBC Burmese that Win Naing Kyaw, a former army major, and Thura Kyaw, a clerk at the European desk of Burma's foreign ministry, had been sentenced to death by a court in Rangoon on Thursday.
They were found guilty of leaking information about government visits to North Korea and Russia, which reportedly took place in 2008 and 2006.
The two men were also convicted of leaking details of a network of tunnels reportedly being built in Burma.
It is thought the tunnels were built to house communications systems, possible weapons factories and troops in the event of an invasion.
The third man, Pyan Sein, was given 15 years in prison on Thursday.
Burma still has capital punishment, but it has not carried out executions in recent years.