The ban and warning, reported by the student news agency ISNA and official IRNA agency, came as a leading reformer spoke of an imminent "important meeting".
Muhammad Reza Khatami's comment fuelled speculation that supreme leader Ayat Allah Ali Khamenei might intervene in the conflict between conservatives and reformists.
Our correspondent said the meeting between Khamenei and the Iranian President Muhammed Khatami had expanded to include the president of the Iranian parliament, Mahdi Karubi, the head of the judicial authority, Mahmud Shahrudi, and the president of the Guardian Council, Hashmi Rafsanjani.
Earlier, reformist legislators said on Tuesday Khamenei opposed delaying this month's parliamentary election despite government objections that the vote would be unfair because of the exclusion of hundreds of aspiring candidates.
One of five lawmakers, who spoke to Reuters on condition of anonymity, said Khamenei, who has the final say on all state matters, "wants the election to be carried out as planned".
Khamenei wants the election to
be carried out as planned
Khatami's pro-reform government has called for the 20 February election to be postponed, arguing the disqualification of more than 2000 reformist candidates by a hardline watchdog meant the vote would lack legitimacy.
Students, a driving force behind the embattled reformist movement, have largely kept out of the three-week old political struggle.
But on Sunday the pro-democracy Islamic Association of Tehran's branches in the main and medical universities said they had sought a permit to stage a gathering at the gate of the capital's main campus on Wednesday.
"No gathering will be allowed outside the entrance of Tehran University," ISNA quoted Ali Taala, director of political and security affairs for the Tehran region as saying.
"No authorisation for a rally at that spot has been issued for several years because of traffic problems in the district," he added, implying that a demonstration could be organised in other circumstances.
On Tuesday, about 250 students gathered within Amir Kabir university in Tehran to express their solidarity with the reformists, some of whose MPs turned up to ask their backing. Some students unfurled banners calling for a referendum and an election boycott.
"To take part in such elections is to legitimise a regime which does not respect the people's rights," said student Mahdi Habibi.
Posters of late Cuban activist
Che Guevara were seen at a rally
Muhsin Armin, one of the 87 barred MPs, called on students to block the election of a "puppet parliament" under which "we will no longer have a free press, nor freedom to defend the rights of jailed students".
Last summer, students sparked a nationwide security crackdown when they led anti-regime protests. Since deadly street riots in 1999, authorities have tried to confine student protesters to their campuses.
Tuesday's ominous warning to reformist papers came from prosecutor Said Mortazavi, who shut down dozens of papers when he was at Iran's press tribunal.
Iranian newspapers expected to be warned about the election crisis coverage include: Shargh, Yas-e No, Nassim-e Sabah, Tossee, Aftab-e Yazd, Etemad, Hambasteghi and Mardom Salari
IRNA quoted the culture ministry, which oversees the press, as saying Mortazavi had written to the ministry asking it to warn the newspapers Shargh, Yas-e No, Nassim-e Sabah, Tossee, Aftab-e Yazd, Etemad, Hambasteghi and Mardom Salari.
An Iranian journalist noted for his support for press rights has also been summoned before a judge over his harshly critical coverage of the crisis.
Friends said Mash Allah Shamsolvaezin had been accused of "spreading confusion among the public".
Shamsolvaezin was jailed in the past and had three of his papers closed by the courts. Several reformist papers have run his comments on the elimination of the reformist candidates by the Guardians Council.