TEHRAN - Iran said on Saturday the U.N. atomic watchdog had confirmed its nuclear programme was peaceful and vowed to resist political pressure to change it, a news agency reported.

The International Atomic Energy Agency (IAEA) report on Friday said Iran had slowed its expansion of uranium enrichment and met some demands for transparency but added that allegations Tehran had researched how to build atom bombs looked credible.

The IAEA report will form the basis for talks on September 2 of six major powers to look into harsher U.N. sanctions against Iran over its enrichment of uranium which the West fears is intended for making nuclear weapons.

The report emphasized ... that Iran's nuclear activities are peaceful, Iran's envoy to IAEA Ali Asghar Soltanieh told the semi-official Fars news agency.

It shows Iran has continued its cooperation with the agency ... but at the same time will not accept any political pressure to take measures beyond its legal commitments, he said.

The West believes Iran wants to produce atomic bombs under cover of a civilian nuclear fuel programme but Tehran rejects the charge saying its nuclear work is a peaceful means to generate electricity.

President Mahmoud Ahmadinejad, re-elected in a disputed June presidential election, has signaled tougher foreign and nuclear policies in the next four years.

U.S. President Barack Obama has set a September deadline for Iran to agree to international talks about its uranium enrichment activities.

But the political turmoil in Iran since the June 12 vote, which Ahmadinejad's rivals say was rigged, is preoccupying Iranian leaders, making it harder for them to deal with other issues.

An official from the White House said the IAEA report showed Iran effectively continues to expand its nuclear programme and continues to deny the agency full cooperation.

In its report, IAEA urged Iran to re-engage with the agency to clarify and bring to a closure questions related to the alleged studies (of military dimensions).

Diplomats said a summary of the agency's investigation into alleged military dimensions to Iran's nuclear activity was unusually blunt, laying credence to intelligence material, and would stiffen Western resolve to seek tougher sanctions.

The IAEA said Iran was enriching uranium with about 300 fewer centrifuges than the almost 5,000 operating at the time of the last IAEA report, the first such scaleback in around three years. The report did not venture possible reasons.

However, the confidential U.N. watchdog report said Tehran had raised the total number of installed, though not all enriching, machines by some 1,000 to 8,308.

Enriched uranium can be used both for fuelling power plants and, if desired, for making bombs.

(Writing by Zahra Hosseinian; editing by Michael Roddy)