WARSAW (Reuters) - Poland on Friday approved a law making chemical castration mandatory for pedophiles in some cases, sparking criticism from human rights groups.

Under the law, sponsored by Poland’s center-right government, pedophiles convicted of raping children under the age of 15 years or a close relative would have to undergo chemical therapy on their release from prison.

“The purpose of this action is to improve the mental health of the convict, to lower his libido and thereby to reduce the risk of another crime being committed by the same person,” the government said in a statement.

Prime Minister Donald Tusk said late last year he wanted obligatory castration for pedophiles, whom he branded ‘degenerates’. Tusk said he did not believe “one can use the term ‘human’ for such individuals, such creatures.”

“Therefore I don’t think protection of human rights should refer to these kind of events,” Tusk also said.

His remarks drew criticism from human rights groups but he never retracted them.

“Introducing any mandatory treatment raises doubts as such a requirement is never reasonable and life can always produce cases that lawmakers could never have even dreamt of,” said Piotr Kladoczny from the Helsinki Foundation of Human Rights.

“If somebody is of sound mind, we punish him. If he is sick, we try to cure him -- that’s how it works in Polish law. This bill introduces both approaches. As far as I know, this makes our law the strictest in Europe on this issue,” Kladoczny said.

The bill, which also increases prison sentences for rape and incest, must still be approved by the upper chamber of parliament. This is seen as a formality as Tusk’s Civic Platform party holds a majority of its 100 seats.