Iran on Tuesday lashed out at "politically motivated" Western accusations against Tehran over US plot claims, its human rights record and nuclear activities.

Foreign ministry spokesman Ramin Mehmanparast said fresh UN accusations of rights abuses in Iran were part of a Western campaign against the Islamic republic following the US assassination plot allegation and increased pressure over Tehran's nuclear programme.

"The nuclear issue and human rights (issue), as well as the newly expressed (US plot) accusations, show that these moves are politically motivated with the sole aim of imposing more pressure on our nation," he told reporters.

He was responding to a new report by a UN special rapporteur on Iran's human rights situation, Ahmed Shaheed, that highlighted the secret execution of more than 300 prisoners, among a raft of other abuses.

The document was obtained by AFP and other media ahead of its presentation to the UN General Assembly on Wednesday.

The UN Human Rights Committee in Geneva lambasted Iran on Monday for failing to say how many prisoners were executed and for giving few details about the alleged crimes of those sentenced to capital punishment. It also criticised the denial of women's rights.

Mehmanparast said the UN report and added pressure on Iran being mounted by the United States at the International Atomic Energy Agency were "not unrelated to the pressures they (Western nations) are trying to exert on our nation."

He said the US allegations that Iranian officials had a hand in a plot to assassinate the Saudi ambassador to Washington were "baseless" and that Iran had been shown no evidence to support the claims.

"We have not directly received anything yet, despite having asked twice for documents," he said. "If they claim something, they should provide proof."

The United States has said it would allow Iranian diplomats to visit the Iranian-American man it is keeping in custody as its chief suspect in the alleged plot.

But Mehmanparast said "it has not yet been mentioned how this consular access will be provided."

The ministry spokesman said US officials were "jumping to conclusions" with the plot claims and were making "unfounded allegations" in a bid to disrupt Iran's relations with other countries in the Middle East.

Iran has repeatedly denied any involvement in the alleged plot.

On Monday, Foreign Minister Ali Akbar Salehi said said Iran was "ready to examine" the information behind the US accusations.

But President Mahmoud Ahmadinejad said no probe would be launched.

"Why should we investigate?" Ahmadinejad asked in a television interview with Al-Jazeera International.

"Every day the United States launches a new accusation against Iran. This position by the United States is wrong. If they think that by applying pressure they will get results they are wrong," he said.