* Around 100 prisoners to be released-President's Office

* Watchgroup says 52 are political prisoners

* New Zealand citizen due for release-family

Myanmar began releasing the first of about 100 prisoners on Friday, many of them political detainees, days before a parliament dominated by democracy champion Aung San Suu Kyi's party sits for the first time after an election win in November.

The freeing of some political prisoners by the outgoing administration of President Thein Sein comes after US Assistant Secretary of State Antony Blinken urged Myanmar to free all political prisoners during a visit on Monday.

The amnesty gives a last-minute boost to the legacy of Thein Sein, whose semi-civilian government in 2011 replaced a junta that had run Myanmar for 49 years, ushering in a series of political and economic reforms.

"There were 52 political prisoners among those released today," said Bo Kyi, joint secretary of political prisoner watchdog Assistance Association for Political Prisoners (AAPP).

According to Bo Kyi, this leaves 77 political prisoners behind bars and 408 awaiting trial.

Zaw Htay, a director at the president's office, said on his Facebook page that 102 prisoners would be freed. It was unclear how many had already been freed and whether all of them were political prisoners. Zaw Htay also said that 77 death sentences would be reduced to life imprisonments.

Phillip Blackwood, a New Zealand citizen jailed in Yangon's notorious Insein prison in March for two and a half years for insulting religion, was also due to be freed, according to his family.

He had used a psychedelic image of Buddha wearing headphones to promote a party at a Yangon bar in a case that threw a spotlight on the country's hardline Buddhist nationalists who championed the harsh sentencing.

"We've been told he will be released within the next few days or it could be up to a week," said Angela Blackwood, the prisoner's mother, when contacted by phone.

It was unclear whether two Myanmar citizens jailed along with Blackwood would be released.

Myanmar's incarceration of more than 2,000 journalists, activists, politicians and even comedians during decades of military rule was a key factor behind Western sanctions.

"While we recognize this as an important step, we remain concerned that there are still many individuals who remain jailed or on trial for simply exercising their right to freely express themselves," the US Embassy in Yangon said in a statement, calling for their release.

As others were walking free on Friday, NGO worker Patrick Khum Jaa Lee, arrested in October for a Facebook post deemed insulting to the military, was sentenced to six months in jail at a court in Yangon. With time served, he will be eligible for release in April.

"The military is sending a very clear message that whoever tries to touch or criticize them, they will seriously take action," said May Sabe Phyu, his wife and a prominent women's rights activist.