YANGON (Reuters) - Myanmar's junta has freed six prisoners of conscience including Thet Naung Soe, a student sentenced to 14 years in jail for staging a solo protest outside Yangon's City Hall in 2002, an opposition lawyer said on Friday.

The five men and a woman were freed from Yangon's notorious Insein prison on Thursday shortly after a visit by U.N. human rights envoy Paulo Sergio Pinheiro, who was in the former Burma investigating September's bloody crackdown on democracy protests.

Aung Thein, a member of the opposition National League for Democracy's (NLD) legal advisory committee, said five of those freed were NLD members.

Thet Naung Soe was said to have been in poor physical and mental health as a result of his time in prison.

Official media say all but 91 of the nearly 3,000 people arrested in September and October have been released, although a Yangon-based diplomat said this week that around 1,000 were still behind bars.

This estimate does not include the 1,100 political prisoners that human rights groups and the United Nations say were being held by the junta before the crackdown, in which at least 10 people -- and probably many more -- were killed.

Pinheiro visited Insein on Thursday at the end of his five-day visit, the first time he has been given a visa in four years.

He met several dissidents, including Win Tin, the 78-year-old journalist who has the dubious honour of being Myanmar's longest-serving political prisoner after 18 years in jail.

However, Pinheiro failed to meet top activist Min Ko Naing, leader of a ruthlessly suppressed mass uprising against military rule in 1988 as well as initial protests in August this year against shock fuel price increases.

(Reporting by Aung Hla Tun; Writing by Ed Cropley; Editing by Darren Schuettler)