DUBAI (Reuters) - A group of 13 human rights organizations urged the British government to call for the release of three Bahrainis detained in the Gulf State, saying they were being punished because they were relatives of a London-based activist and his wife.

In a letter sent to Foreign Secretary Boris Johnson, the group that includes Amnesty International and UK legal charity Reprieve called for the release of Sayed Nazar Alwadaei, Hajar Mansoor Hasan and Mahmood Marzooq Mansoor.

The three are relatives of Sayed Ahmed Alwadaei and his wife Duaa Alwadaei. Sayed Ahmed Alwadaei is the director of advocacy at the Bahrain Institute for Rights and Democracy, a Britain-based group campaigning for political change in Bahrain.

The three were arrested in March in Bahrain while Sayed Ahmed Alwadaei was attending the 34th session of the UN Human Rights Council in Geneva.

“We therefore urge your government to request Bahrain to immediately release Mr and Mrs Alwadaei’s relatives ahead of their October 30 trial and drop all charges against them,” said the letter sent on Thursday.

It called the case “part of a pattern of abuse and harassment against human rights defenders and their families in Bahrain”. The letter said the three detainees are facing up to three years in jail.

“Bahrain is punishing his innocent family as retribution for his peaceful activism,” said Maya Foa, director of Reprieve.

Bahrain’s government officials could not be immediately reached for a comment.

Sayed Ahmed Alwadaei’s family members have been under the spotlight of Bahrain’s authorities since he took part in protest against the attendance of the Gulf state’s king at a royal horse show in Britain.

King Hamad attended the Royal Windsor Horse Show last year, and the state-run Bahrain News Agency BNA published his photographs with Britain’s Queen Elizabeth II.

Bahrain, which has a Shi’ite Muslim majority population and is ruled by a Sunni royal family, has seen unrest since the “Arab Spring” protests across the region in 2011.

Many of Bahrain’s Shi‘ites say they suffer discrimination, which the government denies. It accuses Shi‘ite power Iran of fomenting unrest on its soil, a charged Tehran denies.