DUBAI (Reuters) - A Bahrain court sentenced three family members of a prominent activist to jail terms on weapons charges on Monday, rights group the Bahrain Institute for Rights and Democracy (BIRD) said and accused authorities of using torture to extract confessions.

In a separate case, Bahrain’s Public Prosecutor announced on Monday that it had sentenced 19 unnamed defendants to prison terms for contacts with a banned party it says is backed by Iran and involved in militant attacks.

The cases underscore how authorities in the kingdom is cracking down on perceived threats nearly six years after pro-democracy protests inspired by the “Arab Spring” were quashed with help from Gulf Arab neighbors. Bahrain hosts the U.S. Fifth Fleet.

Sayed Ahmed Alwadaei, BIRD’s head of advocacy, said his relatives were convicted based on confessions gained by torture and said the court was persecuting the family for his activism.

Alwadaei’s mother-in-law Hajer Mansoor and brother-in-law Sayed Nizar Alwadaei were each sentenced to three years in jail for planting a “fake bomb,” BIRD said, while his cousin Mahmood Marzooq was sentenced to a month and half for obtaining a knife.

Representatives of the Bahraini government did not immediately respond to a Reuters request for comment.

Alwadaei, who is based in Britain, said he believed the case against his relatives was motivated by his human rights work and especially a protest last year in which he took part against the attendance of Bahrain’s king at a royal horse show in Britain.

“I was distraught to see my family suffer torture, persecution and interrogations about my activities ... I will not rest until they are freed,” Alwadaei said in a statement.

Bahrain, which has a Shi’ite Muslim majority population and is ruled by a Sunni royal family, denies clamping down on dissent.

The government, citing years of deadly bombing and shooting attacks against its security forces, says it faces a militant threat backed by arch-foe Iran.

According to the prosecutor, a court sentenced eight defendants to life terms, nine to 15 years and two for ten years for “conspiring with a foreign state and terrorist organisation working for its interests and receiving funds from it to carry out hostile acts and in order to harm national interests.”

Fifteen of the defendants had their citizenship revoked.

The group it cited was the Islamic Wafa Movement, a political party that is banned in Bahrain and which authorities accuse of receiving money and support from Iran.

A leader in Wafa, Murtada al-Sanadi, an exiled Bahraini cleric who was named by the United States this year as a “specially designated global terrorist” and appears to be based in the Iranian city of Qom.