Tehran: Opposition leader and former premier Mir Hossein Mousavi vowed a "year of perseverance" in his fight against the government, in an Internet message on Friday to mark the Iranian New Year.
European states also said Tehran should stop censoring the Internet and jamming satellite broadcasts to Iran.
Mousavi, who remains steadfast in rejecting last June`s re-election of President Mahmoud Ahmadinejad, said a "retreat would be treason to Islam, the nation and to the blood of the martyrs."
"We will face issues and problems in (the Iranian year to March 2011)," Mousavi said on his website, adding that the issues were "rightful" popular demands.
"These demands will continue and the New Year will be the year of perseverance for this rightful and legal demand," he said of Nowrouz, which starts on March 21 and marks the arrival of spring.
Once seen as a pillar of the Islamic regime, Mousavi is now a bitter critic of the hardline leadership, along with fellow prominent opposition figure Mehdi Karroubi.
One of the worst political crises in 30 years erupted when Mousavi, Karroubi and hundreds of thousands of their supporters took to the streets after Ahmadinejad`s re-election, charging that the poll had been massively rigged.
EU states said on Friday Iran should stop jamming broadcasts and censoring the web, following a crackdown on the media after the protests in which it also resorted to communications blackouts.
Nearly 70 foreign radio and television stations that transmit to Iran via the Eutelsat satellite were jammed on February 11, the 31st anniversary of the Islamic Revolution, they said.
Reformist former president Mohammad Khatami, a strong supporter of the opposition, meanwhile, called for electoral changes and political prisoners to be freed.
"We should learn our lesson from past events and choose a different path," the website Parlemannews.ir quoted Khatami as telling a group of reformists.
"Several issues can be solved if prisoners are freed, political movements enjoy legal freedom, criticism is allowed within legal boundaries (and) the ground is prepared for healthy and free elections."
However, a supporter of both Khatami and Mousavi was reported jailed on Friday after an appeals court upheld a one-year sentence for spreading anti-regime propaganda.
Opposition website kaleme.com said Hossein Marashi "was taken to Tehran`s Evin prison on Thursday" and banned from engaging in party political activity for six years.
Mousavi also lashed out at the government`s handling of the inflation-hit economy, predicting the year ahead would see unemployment and poverty mount as investment wanes.
"The adventurist policies, which lack wisdom, have created a threatening situation for us," he said.
"We are in the worst situation when it comes to foreign policy and international relations, and we will witness more sanctions and pressure," Mousavi predicted.
Washington has been bolstering efforts to garner international support for a fourth round of UN sanctions against Tehran for doggedly pursuing its nuclear programme.
Hardline cleric Ahmad Khatami, who has repeatedly lashed out at the opposition, urged Iranians in his Friday prayer sermon to remain "alert" after the disputed election.
"Last year`s events were complex, but there were lessons to be learned. The most important lesson was that we must be alert," he said at Tehran University.