Human Rights Watch (HRW) has called on Iran to "grant immediate access to a specialist medical facility”, to prominent opposition figures "and end their house arrest".

The former presidential candidates -- Mehdi Karrubi and Mir Hossein Musavi and his wife, Zahra Rahnavard -- have been under house arrest in Tehran since February 2011 for challenging the government over the disputed 2009 presidential vote and also for highlighting alleged human rights abuses.

“Iranian officials have deprived Musavi, Karrubi, and Rahnavard of their most basic rights for more than six years, all without a judicial order or even the pretense of due process,” Sarah Leah Whitson, HRW's Middle East director, said in an August 2 statement.

“Iran’s authorities should stop denying Musavi and Karrubi the care they need, grant immediate access to a specialist medical facility, and end their house arrest,” it said.

Karrubi was hospitalized for the second time in a week due to a heart condition, his wife said on July 31.

Musavi and Rahnavard are also suffering from health problems, their daughters have said.

HRW, also called on President Hassan Rouhani to honor his promises of improving the human rights situation in Iran.

“As President Rouhani begins his second term on August 5, he should demonstrate that he takes his promises to his fellow citizens for more rights and legal protections seriously,” Whitson said. “A good place to start would be to free Mehdi Karroubi, Mir Hossein, and Zahra Rahnavard from house arrest and to see that they get the health care they need.”