DUBAI (Reuters) - Prominent Bahraini rights campaigner Nabeel Rajab, in detention for alleged remarks criticizing the kingdom's involvement in the war in Yemen and its prison system, was taken to hospital with a heart condition, supporters said on Twitter.

A government official said Rajab had undergone medical checks in hospital and described his condition as normal.

The 51-year-old activist, founder of the Bahrain Centre for Human Rights, had been repeatedly imprisoned since pro-democracy protests rocked the Western-allied Gulf island in 2011.

A message on his Twitter account, which is run by his supporters, said Rajab was taken to a hospital by ambulance from prison after he suffered from heart problems.

"Nabeel Rajab at Coronary Care Unit suffering from unprecedented heart problems after 15 days in solitary," another post said, without giving further details.

His wife was quoted by rights group the Bahrain Institute for Rights and Democracy as expressing alarm and blaming poor treatment by Bahraini authorities.

"We raised extreme concern about the effects that isolated detention would have on Nabeel's health and we were ignored. Nabeel never suffered heart problems before. My husband is a human rights defender and does not deserve this treatment," Sumaya Rajab said.

A spokesperson from the prison authority said that Rajab was examined. "Nabeel Rajab, who is held in custody pending further investigations has gone through medical checkup in hospital today. Results show his health condition is normal," the spokesperson said via e-mail.

Rajab was arrested on June 13, nearly a year after he was freed by a royal pardon from a six-month sentence handed out in May 2015 for making alleged remarks deemed insulting to the kingdom's security establishment.

His lawyer said on Sunday he will face trial apparently in connection with tweets which authorities accuse him of making about the kingdom's prison system and its involvement in the war in Yemen, charges that could carry up to 13 years in jail.

Rajab spent two years in jail after being convicted in May 2012 of organizing, and participating in, illegal protests.

Bahrain, where the U.S. Fifth Fleet is based, is pursuing a crackdown on the opposition in a campaign that had also included a court shutting down a main opposition society and a decision to strip the spiritual leader of the island's Shi'ite Muslim majority of his citizenship. [L8N19D29M]

(Writing by Sami Aboudi, editing by Dominic Evans)