The move came as diplomats struggled in Vienna Friday to break a deadlock over a US-backed resolution at the watchdog International Atomic Energy Agency (IAEA) to condemn Iran for hiding atomic activities.
The IAEA was split between a US-led bloc which wants to hint at possible action against Iran for what it says is a clandestine program to develop nuclear weapons, and Non-Aligned states which want to include more praise for Tehran's efforts at cooperation.
Iranian ambassador to the IAEA Pirooz Hosseini had told AFP his country had put back the inspection mission, scheduled to start this week, "due to the approach of the Iranian New Year."
In giving a new date for the inspections, the diplomat said the postponement of at least a month has the IAEA thinking that if the Iranians "really had nothing to hide, this is fully against their interests."
The diplomat said this was giving those like the United States who accuse Iran of hiding a nuclear weapons program "a big pile of ammunition with this move."
The postponement means that the IAEA inspectors will be in Iran "really only a month" ahead of a June board meeting that is to review the Iran situation, based on an IAEA report to be written in May.
The inspectors will have "not enough time" now to get a full report to the June board.
The diplomat said: "If the Iranians don't re-consider, this could be potentially a large problem in the verification process."
The IAEA, which verifies the nuclear Non-Proliferation Treaty (NPT), has since February 2003 been working to determine whether Iran's nuclear program is peaceful, or devoted to secretly developing atomic weapons, as the United States has charged.
Iran signed an additional protocol to the NPT allowing for wider, short-notice inspections in December.
The diplomat said that maybe Iran "felt the agency's inspectors were coming too close to them or wanted to show some political muscle of their own to defy those countries casting strong-worded resolutions condemning them."
IAEA officials refused to comment on the inspection mission.
Iranian Foreign Minister Kamal Kharazi had threatened in Iran this week that the Islamic Republic would end cooperation with the IAEA unless it stopped being "influenced by the Americans".
Hosseini said the delay in the inspection mission was not politically motivated since it was a matter of a vacation in Iran.
But the vacation is only six days and a second diplomat close to the IAEA said "of course it's political", and added that "the delay in inspections will definitely slow down what the IAEA is trying to do."
The first diplomat said the postponed inspection was "likely to have been crucial to major inspections of still open questions such as P-2 (centrifuges to enrich uranium that Iran failed to declare), how far this went, laser enrichment programs, and HEU (highly enriched uranium) programs."
The inspection was also to verify Iran's "suspension of uranium enrichment and other parts of it," the diplomat said, referring to a voluntary suspension by Iran of the manufacture of potentially weapon-grade uranium which the IAEA wants widened to included related activities such a building centrifuges.
In the deadlock over a resolution, a Western diplomat said the problem seemed to be that the United States, which had made concessions to Britain, France and Germany, in softening the text had now "hardened its position" in response to Non-Aligned amendments to make the resolution friendlier to Iran.
The IAEA board meeting, which began Monday, is to continue Saturday.
A diplomat from one of the 13 Non-Aligned Movement (NAM) states on the 35-nation IAEA board said his group, which met with Iran's IAEA representative Wednesday, wanted to "soften the tone" to alienating the Islamic Republic.
The NAM group wants to eliminate what could be a so-called trigger mechanism for moving against Iran: a statement that the IAEA board should in June decide "how to respond" to Iran's omissions in reporting sensitive nuclear technology.