Iranian authorities on Monday detained two daughters of leading opposition figure Mirhossein Mousavi, a former presidential candidate held under house arrest for nearly two years, an opposition-linked website reported.
Mousavi stood in presidential elections in 2009 and was a figurehead of the big street protests over allegations of vote rigging that followed. He is held under house arrest with his wife Zahra Rahnavard.
The Islamic Republic is gearing up for another presidential vote in June and hardline figures have accused opposition forces of plotting a second "sedition" - referring to the last protests that were crushed by security forces.
Security forces went to the home of the couple's daughters Narges and Zahra on Monday morning and detained them, according to Kaleme, an opposition website close to Mousavi. It did not say where they were taken.
The couple have one other daughter and the three sisters wrote in a statement last month that authorities had denied Mousavi and Rahnavard contact with their children for weeks.
Mousavi and Mehdi Karoubi, another opposition figure, were detained after they called their supporters onto the streets for a rally in support of uprisings in the Arab world in February 2011. Hardliners have asked the judiciary to execute both men, but authorities have so far chosen to isolate rather than officially arrest them.
Mousavi, 70, Iran's prime minister in the 1980s, was treated for a heart problem in hospital in August, one of his former senior advisors told Reuters.