Protests over a disputed June 12 election that handed President Mahmoud Ahmadinejad a second term continued on Wednesday, according to unconfirmed reports, despite a police crackdown and calls for nationwide mourning for demonstrators killed in post-election violence.

Iran's supreme leader, Ayatollah Ali Khamenei, appeared to toughen his stance on Wednesday. He vowed not to "back down" in the face of opposition calls for a re-vote.

"In the recent incidents concerning the election, I have been insisting on the implementation of the law and I will be (insisting)," Khamanei said. "Neither the system nor the people will back down under force."

In the streets of Tehran, clashes between demonstrators and security forces continued on Wednesday, according to witness accounts published on the Internet. “At least 5,000 people gathered on Sadeghieh square [in Tehran] and were attacked by Basij militiamen,” says a FRANCE24 Observer  on twitter. On Baharestan square, the situation is “terrible”, according to Persianwiki, another active Web user on Twitter. He claims Basij militias have surrounded demonstrators before charging. Gunshots are said to have been heard, “there are dead people everywhere,” he reports.

Amateur footage released on YouTube and checked by our Observers team show demonstrations in Tehran on Wednesday 24/06

Conservative candidate Mohsen Rezaie, who finished third in the contested presidential race, announced Wednesday his decision to withdraw his official complaint about the vote, underscoring the perception that popular opposition to the poll was unravelling.

In a letter to the Guardian Council, Iran’s top legislative body, he said that he was putting the security of the country above his own interests.

The two other defeated candidates, former Prime Minister Mirhossein Mousavi and reformist cleric Mehdi Karoubi, are pressing on with their complaint of widespread vote-rigging in favour of Ahmadinejad, who reportedly won the election with 63 percent of the vote.

But the candidates’ protests seem to be at a dead end, as both street demonstrations and legal appeals have failed to move the Islamic republic’s establishment to acknowledge substantial voting irregularities.

The Guardian Council has already rejected demands for a re-run of the elections, although it did agree to extend the deadline for lodging complaints by five days. Meanwhile, the Interior Ministry has continued to ban reformist gatherings.

Farhad Pouladi, an AFP correspondent in Tehran reporting for FRANCE 24, said the government also banned a pro-Ahmadinejad protest in front of the British embassy on Wednesday.

“They want to show they are being fair in giving out licenses because they didn’t issue a license for the pro-Mousavi and pro-Karoubi gatherings,” Pouladi said.

Iranian authorities have barred the few foreign reporters who haven’t yet been expelled from attending any gathering.

Nationwide mourning

The largest street protests in Tehran since the 1979 revolution were put down by a united front of Basij militia, Revolutionary Guards and special anti-riot police. The crackdown has cost the lives of at least 17 protesters in two weeks, reducing the number of Iranians willing to take to the streets.

Mousavi, who says he is the rightful victor of the presidential election, is a cautious opposition leader, careful not to give his support to explicitly anti-regime rallies.

“Today there are calls for a gathering in front of the Iranian parliament, but Mousavi said on one of his websites that this gathering is not backed by him,” says the AFP's Pouladi.

But Mousavi's wife, Zahra Rahnavard, posted a statement on her website on Wednesday calling for the authorities to release politicians and protesters arrested in the wake of the contested election.

"It is my duty to continue legal protests to preserve Iranian rights" she said in her statement.

Iranian authorities are also facing a fresh challenge as reformist clerics call for nationwide mourning.

“Karoubi has called for a day of mourning and a gathering [on Thursday] to commemorate those who have fallen,” Pouladi says.

Grand Ayatollah Hossein Ali Montazeri, a former ally of Ayatollah Ruhollah Khomeini turned dissident, called for three days of national mourning for those killed.

“Resisting the people’s demands is religiously prohibited,” Montazeri said in a statement on his website, underscoring a growing rift among the nation’s ruling clergy.

Besides the risk of degenerating into street protests, the days of mourning for the crackdown’s victims might further undermine the supreme leader’s moral authority and weaken the whole regime.

Obama ‘appalled and outraged’

In his strongest statement yet on the subject, US President Barack Obama said Tuesday that he was “appalled and outraged” by Iran’s clampdown.

Obama also reacted to Tehran’s accusations that Western powers were instigating the protests, saying that “this tired strategy of using old tensions to scapegoat other countries won’t work anymore in Iran”.

Britain on Tuesday said that it was expelling two Iranian diplomats in response to Tehran's expulsion of two British envoys as relations hit a new low following Iran's allegations of foreign interference.