Iranian authorities have banned the publication of a letter that called on the country's supreme leader to intervene to break the political deadlock holding up the reform process.
Ayatollah Khamenei and his clique of clerics dominate Iran
The strongly worded letter to Ayatollah Ali Khamenei - signed by 127 members of the pro-reform parliament - warned that time was running out for a peaceful transition.
The National Security Council, the highest body on security issues, is reportedly behind the ban.
The letter was posted on the website of the largest reformist political party, the Participation Front, for only two hours on Saturday before being hurriedly taken down.
Not much time is left... The destiny of our country
can either be dictatorship, or the respect of democratic rules
No other newspapers or news agencies have dared make the letter public - apparently out of fear of stirring a violent response from hardline supporters of Mr Khamenei.
It is the latest move in a political crisis that has been intensifying as reformists become increasingly frustrated by the blocking of new legislation by conservative-controlled bodies.
The deputies who signed the letter said political and social rifts inside the country were coinciding with an external threat, with the emergence of a clear American plan to change the region's geo-political map.
This is, they said, probably the most sensitive time in Iran's recent history.
'Campaign of sabotage'
The letter called for a referendum which would lead to real democracy guaranteeing freedom and dignity.
It accused unelected right-wing institutions of mounting a concerted campaign to undermine the reformist movement and its chief symbol, President Mohammad Khatami, despite the latter's landslide election victories.
It singled out for particular criticism the Guardians Council, a conservative-controlled oversight body that vets all legislation, and the judiciary.
Religious leaders dominate the streets in Teheran, as well as political life
President Mohammad Khatami tried to break the impasse last year by introducing two bills which would enhance his own powers and reduce those of the unelected conservative strongholds.
But the bills were blocked by one of those very bodies, the Guardians Council.
Commentators say the reformists thus face a major dilemma with few options.
The ayatollah has not so far responded officially to the letter, but in his first comments since the appearance of the document, he strongly attacked his critics.
He claimed the Islamic republic was "the most democratic system of government in the world" and accused reformists of showing weakness in the face of foreign threats.
But, BBC regional analyst Sadeq Saba says that despite his defiance the ayatollah is in a difficult position over how to deal with this open questioning of his leadership.
This is especially the case given that most Iranians and President Khatami are believed to support the reformist deputies, says our analyst.