Iran's supreme leader called his country's alliance with Syria a symbol of resistance in the Middle East on Wednesday, seeking to reinforce a key relationship as Tehran fends off continued criticism over its response to post-election unrest.

Visiting Syrian President Bashar Assad exemplified that resistance by criticizing foreign countries for provoking the massive protests that followed Iran's disputed June presidential election. His comments will likely disappoint the Obama administration, which has stepped up diplomatic efforts to pull Syria away from Iran.

"I've come here today to personally convey my warm congratulations to you and the Iranian nation," Assad was quoted by Iran's official news agency as telling President Mahmoud Ahmadinejad, whose re-election was seen as fraudulent by the opposition.

"I believe what happened in Iran was an important development and a great lesson to foreigners," IRNA quoted Assad as saying.

Iran's supreme leader, Ayatollah Ali Khamenei, and other influential hard-liners have attempted to paint the post-election unrest as a plot by the U.S. and other countries to topple the country's Islamic system — charges they have denied.

Khamenei sought to play up fears of the U.S. in talks with Assad, telling the president that "Syria's most important characteristic among Arab countries is its resistance, and that is the reason behind America's animosity," according to IRNA.

Syria is Iran's closest Arab ally, and Tehran is keen on preventing Damascus from migrating closer to the West. Continued Syrian support is especially critical as domestic and international criticism continues over Iran's violent crackdown on opposition supporters following the election.

Much of the international attention surrounding Assad's two-day visit focused on whether he would lobby for the release of Clotilde Reiss, a French academic on trial with more than 100 politicians, journalists and activists accused of trying to engineer a "velvet revolution" to overthrow the Islamic leadership.

Reiss was released last week on bail, but judicial authorities have barred her from leaving the country.

France last week thanked Syria for helping win the release from jail of a French-Iranian employee of the French embassy in Tehran, who is also in the same mass trial. France has long had close ties with Syria, a former colony.

Releasing the French academic could be seen by Iran's leadership as a chance to win some international goodwill after facing allegations of torture and other abuses against demonstrators.

One of the pro-reform challengers in the June 12 vote, Mahdi Karroubi, issued a letter to Parliamentary Speaker Ali Larijani saying he was prepared to meet with top officials, including Ahmadinejad, to present evidence that some protesters were raped in custody. The letter was posted on his party's Web site.

Karroubi, a former parliament speaker himself, has said he has received reports of rapes from detainees released from jail as well as from former military commanders and other senior officials.

But Larijani has rejected Karroubi's claims, and other hard-liners have called for the arrest and trial of Karroubi for making the allegations.

Karroubi slammed Larijani's speedy denial, saying no probe could have been completed that fast. He has also vowed he won't remain silent over the "medieval torture and corruption" in Iran's prisons.

Some conservatives have also demanded a full investigation, leading to splits in Ahmadinejad's base of support.

"I demand from you to hold a meeting ... so that I can personally present my documents and evidence on cases of sexual abuse in some prisons," Karroubi said in the letter.

On Monday, Iran's prosecutor general ordered the closure of the pro-reform newspaper Etemad-e-Melli after it ran articles on Karroubi's rape allegations. Karroubi heads the political party that runs the newspaper. The prosecutor gave no word on the length of the closure.