By Hnin Yadana Zaw

NAYPYIDAW (Reuters) - Myanmar's president on Monday signed into law the last of four controversial bills championed by radical Buddhists but decried by rights groups as aimed at discriminating against the country's Muslim minority.

Myanmar, which will hold its first democratic national poll in more than two decades on Nov. 8, has seen a flowering of anti-Muslim hate speech since the military gave up full power and opened up politics and the economy in 2011.

President Thein Sein signed the Monogamy Bill after it was passed by parliament on August 21, Zaw Htay, a senior official at the president's office, told Reuters. The law was briefly sent back to parliament for review before being signed.

The bill sets punishments for people who have more than one spouse or live with an unmarried partner other than the spouse.

The government denies it is aimed at Muslims, estimated to make up about 5 percent of the population, and some of whom practice polygamy.

The president also signed two other laws, which restrict religious conversion and interfaith marriage, on August 26, Zaw Htay said.

The measures are part of four "Race and Religion Protection Laws" championed by the Committee for the Protection of Nationality and Religion, or Ma Ba Tha.

The laws were dangerous for Myanmar, said an official of New York-based Human Rights Watch.

"They set out the potential for discrimination on religious grounds and pose the possibility for serious communal tension," said Phil Robertson, deputy director of the Asia division of Human Rights Watch.

"Now that these laws are on the books, the concern is how they are implemented and enforced."

In May, the president signed a Ma Ba Tha-backed population control bill that forces some women to space three years between each birth.

The monk-led group has stoked sentiment against Muslims, whom it has accused of trying to take over Myanmar and outbreed its Buddhist majority.

Hundreds of people have been killed in flare-ups of religious violence in Myanmar. In 2012, an incident in Rakhine State led to the displacement of more than 140,000 people, most of them members of the stateless Rohingya Muslim minority.

(Additional reporting and writing by Aubrey Belford in Yangon; Editing by Clarence Fernandez)