By Zahra Hosseinian

TEHRAN (Reuters) - Former President Mohammad Khatami said on Wednesday trial confessions by moderates accused of fomenting post-election unrest were made under "extraordinary conditions" and were invalid, the ILNA news agency reported.

At Tuesday's trial, the fourth since June polls denounced by moderates as fraudulent, senior reformer and Khatami ally Saeed Hajjarian was reported as saying he had "made major mistakes during the election by presenting incorrect analyses."

"I apologize to the Iranian nation for those mistakes."

A prosecutor demanded maximum punishment for Hajjarian accused of acting against national security, a crime which can carry the death sentence.

"These confessions are invalid and have been obtained under extraordinary conditions ... such claims are sheer lies and false," leading reformist Khatami said, according to ILNA.

Also in the dock on Tuesday were several prominent moderate figures, including former Deputy Interior Minister Mostafa Tajzadeh, business newspaper editor Saeed Laylaz, former Deputy Foreign Minister Mohsen Aminzadeh and former government spokesman Abdollah Ramezanzadeh.

All were charged with fomenting huge street protests that followed the June presidential election that returned hard-liner Mahmoud Ahmadinejad; some confessed to "mistakes."

The June 12 vote has plunged Iran into its most serious internal crisis since the 1979 Islamic revolution and has exposed deep divisions in the establishment's ruling elite.

Iranian-American scholar Kian Tajbakhsh was also accused of acting against national security and espionage at Tuesday's trial, charges likely to anger Washington.

NO MASS BURIALS

Analysts see the trials as an attempt by the authorities to uproot the moderate opposition and put an end to street protests that erupted after the election.

Defeated moderate candidates Mirhossein Mousavi and Mehdi Karoubi say the vote was rigged to secure Ahmadinejad's re-election, a charge the authorities deny.

Karoubi has angered hardliners by claiming some imprisoned protesters were raped and abused in jail, a charge government officials have rejected "as baseless."

The reformist website Norooz said last week that "tens" of people were buried in unnamed graves in the largest cemetery in Tehran on July 12 and 15 -- about a month after the election, suggesting those buried had been protestors.

But a former head of Tehran's Behesht-e Zahra cemetery said on Wednesday no "mass burial" had ever taken place there.

A lawmaker said on Tuesday a parliamentary committee was looking into the rumor.

Rezaian said part of the section of the cemetery referred to in the Norooz report, 302, was used to bury unidentified people who were killed in car accidents or by drug overdose.

The losing candidates say 69 people were killed in the unrest but the authorities put the death toll at 26.

Rights groups say hundreds of people, including senior pro-reform politicians, journalists and activists, have been detained since the election. Many are still in jail.

For a story on Iran's nuclear diplomacy, click [nLP438638]

(Writing by Zahra Hosseinian; Editing by Ralph Boulton)