Iranian authorities have taken senior opposition leaders Mir Hossein Mousavi and Mahdi Karroubi to prison in Tehran, a reformist website has reported.
Kaleme.com said Mr Mousavi, his wife Zahra Rahnavard, Mr Karroubi and his wife, Fatemeh Karroubi, were transferred to Heshmatieh prison in the Iranian capital. The men had been under house arrest for more than two weeks. The report said it was not immediately clear when they were transferred to the prison.
The move would mark a major escalation of Iran's political crisis amid defiant calls from the opposition to stand up to the ruling system.
Activists and opposition members have demanded Mr Mousavi and Mr Karroubi be released, vowing to stage demonstrations every Tuesday until they are freed.
The semi-official Fars news agency, which is close to the powerful Revolutionary Guard, denied that Mr Mousavi and Mr Karroubi had been jailed. Fars quoted an unnamed judiciary official as saying the two opposition leaders were still under house arrest and had not been allowed to leave their homes or contact the outside world.