Tehran - The website Facebook has not been blocked for political reasons but rather morale problems, a chief opposition presidential candidate said Monday.

The labour news agency ILNA had reported that Facebook was blocked for Iranian internet users to prevent propaganda for moderate Mir-Hossein Moussavi, who is the main challenger of Iranian President Mahmoud Ahmadinejad.

"As far as I know the blocking of this website was due to morality problems but during this pre-election period, many issues are interpreted as political," opposition candidate Mehdi Karroubi said in a news briefing in Tehran.

Facebook, one of the most popular websites in Iran, was surprisingly unblocked earlier this year by the Iranian judiciary and since then the number of Facebook members inside Iran has increased dramatically.

The website was blocked again last Saturday and ILNA, which supports Moussavi in the June 12 presidential election, denounced the action as a political move by Ahmadinejad's government against Moussavi.

"Blockings and filtering of websites are not linked to the government but to the judiciary and a special committee there in charge of fighting moral abuse in internet," an internet provider in Tehran said.

Besides pornographic and erotic websites, also political and social networking sites such as Orkut and Facebook, are filtered in Iran as the country's clergy consider these sites as "Western cultural invasion" aimed at deviating the Iranian youth from spirituality and decency.

"Also Ahmadinejad is harmed by the recent blocking of Facebook because also his supporters had started a widespread campaign on that Facebook, even more than Moussavi and Karroubi," the internet provider said.

Right after blocking Facebook, Iranian internet users distributed proxies to break the state-imposed filter of the website and make Facebook available again.

Karroubi said that especially during the pre-election days when international attention is focused on the Islamic republic, Iranian officials should show more tolerance.

"During these sensitive days, many issues could be politicized and eventually harm the country," the moderate cleric said.

Iranians under the age of 25 comprise more than half of the 46.2 million eligible voters and therefore all four candidates - Ahmadinejad, Karroubi, Moussavi and Mohsen Rezaei - are trying to attract them in their election campaigns.

According to official figures released by the communication ministry, the number of internet users in Iran has increased to 23 million out of a total population 70 million Iranians.(dpa)