Iran will from next month ban banknotes which have been scribbled upon, Iranian media reported on Thursday, a move one conservative website said was in response to the appearance of political slogans on some of them.

Expressions in support of moderate opposition leader Mirhossein Mousavi, such as "Oh Hossein, Mirhossein", have occasionally been cropping up on the Islamic Republic's banknotes since its disputed election in June.

Other, non-political scribbles are frequently seen on various denominations, which all carry the image of late revolutionary leader Ayatollah Ruhollah Khomeini.

"Banknotes on which there are writings or are stamped or have any additional signs will be invalid," the Jam-e Jam daily quoted central bank official Ebrahim Darvishi as saying.

He called on the public and shop owners not to accept such notes from January 8, it said. State radio also carried the report.

The Ayande website, seen as close to conservative politician Mohsen Rezaie, said in a headline about the move: "The central bank's reaction to the writing of slogans on banknotes."

In October, daily Mardomsalari quoted Tehran city council member Morteza Talai as calling for the invalidation of notes "with the slogans and messages of counter-revolutionaries," an apparent reference to Mousavi supporters.

Iran plunged into political turmoil in June after a presidential poll which the opposition said was rigged to secure the re-election of hardline President Mahmoud Ahmadinejad. The authorities deny the vote rigging charges.

Despite arrests and crackdowns, opposition supporters have continued to stage sporadic rallies over the last six months.

Tension has increased again this month, with opposition websites on Wednesday saying security forces clashed with supporters of a late dissident cleric at a memorial service for him in the city of Isfahan.

"Montazeri is not dead," said a slogan on an IR20,000 note (about $2) seen this week, after Saturday's death of Grand Ayatollah Hossein Ali Montazeri, a fierce critic of the hardline authorities, at the age of 87.

His death occurred in the tense run-up to Ashura on December 27, a politically important Shi'ite religious commemoration that offers the opposition another opportunity to show its strength.

Police chief Esmail Ahmadi-Moqadam said his force would "firmly" confront protesters if they caused destruction and disorder, the official Irna news agency reported.

"As long as the behaviour of the protesters is not accompanied with lawlessness, destruction and rebellion we will be satisfied with issuing warnings," he said.

Ayande said that every year millions of damaged banknotes are withdrawn and replaced with new ones. State radio said it cost IR400 to replace one of them. – Reuters