Iran said to tighten restrictions on ex-president
Khatami has been banned from appearing in the media since mass protests against the government in 2009-2010, but continues to wield considerable power behind the scenes.
The opposition Kalemeh website said the Special Clerical Court had sent Khatami a letter asking him "not to take part in any political ceremonies and publicity for three months".
This was said to include any meetings, theatre performances and concerts, and barred individuals, government and seminary officials and student union members from meeting with him.
The new restrictions were first revealed by Khatami's nephew Mohammad Reza Tabesh, a member of parliament, earlier this week.
The letter was said to have been signed by the head of the Special Clerical Court, Ebrahim Raisi, the hardline runner-up in this May's presidential election.
The conservative Fars and Mehr news agencies said on Thursday that unnamed officials had denied the existence of the letter or the new restrictions.
But outspoken member of parliament Ali Motahari criticised the new measures, saying they were illegal without proper consultation with Khatami or his lawyers.
"We have a good constitution and the parliament has also devised good laws but some councils and institutions such as the Special Clerical Court bypass the constitution and the parliament and drag the country towards autocracy," he said in comments carried by the semi-official ISNA news agency.
"Imposing more restrictions, at a time when public opinion is opposed to the continuation of the house arrest is regrettable," Motahari added.
He was referring to the house arrest of two other opposition leaders, Mir Hossein Mousavi and Mehdi Karroubi, who have been in detention since 2011 for their role in the anti-government protests.
Motahari also said it would give another excuse for the United States to accuse Iran of human rights abuses at a time when Washington is threatening to pull out of the nuclear deal between Tehran and world powers.
"Have those who made this decision done so out of ignorance, or do they have a plan to bring the JCPOA (nuclear deal) to an end sooner?" he asked.