"Based on parliament's investigations, detainees have not been raped or sexually abused in Iran's Kahrizak and Evin prisons. Such claims are totally baseless," Iran's state television quoted Ali Larijani as saying.
Defeated moderate candidate Mehdi Karoubi said some protesters, both men and women, had been raped in prison.
Many of the post-election detainees were held in south Tehran's Kahrizak prison, built to house people breaching vice laws. At least three people died in custody there.
The abuse allegations have divided hardline politicians, many of whom backed President Mahmoud Ahmadinejad's re-election.
A committee set up by losing candidates Karoubi and Mirhossein Mousavi to pursue the issue submitted a list of 69 people killed in protests to parliament on Monday. The list contradicted the official figure of 26 deaths.
Defeated conservative presidential candidate Mohsen Rezaie said officials in charge should be put on trial.
"If ... reports about the mistreatment and abuses of detainees and protesters are proved, all officials in charge should at least be sacked and tried in court," Rezaie was quoted by the semi-official ILNA news agency as saying.
"And a day of national mourning should be declared."
Rights group Amnesty International urged Iran to allow international observers to monitor the trials of more than 100 people accused of involvement in the protests that followed the election.
'Show trial'
"The trial now going on in Tehran appears to be nothing but a "show trial' through which the supreme leader and those around him seek to de-legitimize recent mass and largely peaceful protests and convince a very skeptical world that Mahmoud Ahmadinejad was re-elected fairly for a second term as president," said Amnesty Secretary-General Irene Khan.
German Foreign Ministry spokesman Andreas Peschke said EU countries had agreed on Monday to summon the Iranian ambassadors in all 27 capitals to voice concerns about the trials.
"This was an act that was previously discussed among the EU-27 ... The agreement was that the Iranian ambassadors in all 27 capitals be summoned," Peschke said.
Washington, its European allies and leading Iranian reformers have rejected the mass trials as a "show."
The fallout from the post-election unrest further cloud prospects of Iran accepting U.S. President Barack Obama's offer of direct talks on Iran's nuclear program.
In the second mass trial to open within a week, on Saturday a court charged a Frenchwoman, two Iranian staffers at the British and French embassies and dozens of senior moderates with spying and plotting to overthrow clerical rule.
The French embassy agreed to provide bail to secure the release of the French woman, teaching assistant Clotilde Reiss, the official news agency IRNA reported on Wednesday.
The semi-official Fars news agency reported that Reiss could not leave Iran if she was released on bail.
"Reiss is under arrest. But her trial procedure is finished. Any decision on whether she should be released on bail until the sentence is issued ... depends on the judge of her case," Fars quoted Tehran prosecutor Saeed Mortazavi as saying.
Last month Supreme Leader Ayatollah Ali Khamenei ordered the closure of the "sub-standard" detention center at Kahrizak. Iranian authorities have acknowledged some protesters were tortured there and said its director had been jailed.
Conservative Larijani called on Karoubi to submit to parliament evidence for his rape allegations. Parliament's reformist minority also asked detainees to report cases of abuse, ILNA reported.
The hardline Kayhan daily urged the judiciary to arrest Karoubi if his charges were proved to be wrong.
"If Karoubi can not prove the allegations then he should be punished without any consideration," said Hossein Shariatmadari, chief editor of the daily, who is appointed by Khamenei.
Karoubi's son said his father had evidence to prove his claims, the Etemaddemelli website quoted Hossein Karoubi as saying.
Hardliners Divided
The opposition says the election was rigged, a charge denied by Iranian authorities, including Khamenei, who has accused Western powers of fomenting the unrest.
State radio said 215 of Iran's 290 lawmakers urged Ahmadinejad to reconsider ties with the United States, France and Britain for their "interference" in Iran's state matters.
A hardline lawmaker said Ahmadinejad was to be blamed for any possible mistreatment in prisons, adding "If we suppress people we will be destroying the system with our own hands."
"We should investigate crimes against detainees and the key responsibility is with two people: the president and the judiciary chief," said Ahmad Tavakkoli, who supported Ahmadinejad's first-term presidency, Iranian media reported.
Another hardline lawmaker criticized harsh methods used by security forces over the unrest. Some 4,000 people were arrested and at least 200 people remain in jail, including activists, senior moderate politicians, lawyers and journalists.
"Some extreme measures were taken by security forces when dealing with protesters," Ali Motahari told the Etemad-e Melli newspaper.
