VIENNA (Reuters) - Iran on Thursday stood by its decision to deny U.N. nuclear inspectors access to sites where they have questions about past activities, arguing that the agency's case is based on "fabricated" Israeli intelligence.

The International Atomic Energy Agency, which is policing Iran's troubled nuclear deal with major powers, sounded an alarm on Tuesday over a lack of Iranian cooperation in clearing up what the IAEA suspects are undeclared activities and materials dating back to the early 2000s. Iran has denied it access to two sites.

Diplomats who follow the IAEA say the decision to inspect those sites to take environmental samples was based at least in part on a trove of documents Israel says its intelligence agents seized in Iran. Israel calls it an "archive" of past activities.

"The Islamic Republic of Iran does not want to set a bad precedence by giving legitimacy to such alleged information," Iran's mission to the IAEA in Vienna said in a statement.

The U.N. nuclear watchdog says it does not take information handed to it at face value and vets it thoroughly before deciding whether to act upon it. Iran granted the IAEA access last year to another site Israel has pointed to, a place Israeli Prime Minister Benjamin Netanyahu called a "secret atomic warehouse" in Tehran.

IAEA inspectors found uranium traces at that site, which Iran has described as a carpet-cleaning facility. The Islamic Republic has yet to give a satisfactory explanation for how those traces got there.

As for the sites to which Tehran has denied nuclear inspectors access, Iran says the agency's case for going there was too flimsy, even though the IAEA says it has the authority to carry out snap inspections anywhere it needs to. Those so-called "complementary accesses" are often at short notice.

"Copies of papers presented to Iran by the agency as the basis for its requests are neither authentic nor related to the open-source, but rather claimed by the Israeli regime to have been acquired through a so-called secret operation," the statement said.

"The Islamic Republic of Iran believes that merely forwarding some papers based on the intelligence services' fabricated information is not consistent with the agency's Statute, Comprehensive Safeguards Agreement, and the Additional Protocol," it said, referring to texts governing the IAEA's mission and activities.

"Therefore, it does not entitle the agency (to) such requests, nor creates any obligation for Iran to consider such requests."