Iran told the United Nations nuclear watchdog on Thursday that it would not accept a plan its negotiators agreed to last week to send its stockpile of uranium out of the country, according to diplomats in Europe and US officials briefed on Iran’s response.

In public, neither the Iranians nor the watchdog, the International Atomic Energy Agency, revealed the details of Iran’s objections, which came only hours after Iran’s President Mahmoud Ahmadinejad insisted that “we are ready to cooperate” with the West.

But the European and US officials said that Iranian officials had refused to go along with the central feature of the draft agreement reached on October 21 in Vienna: a provision that would have required the country to send about three-quarters of its current known stockpile of low-enriched uranium to Russia to be processed and returned for use in a reactor in Tehran used to make medical isotopes.

US officials said they thought that the accord would give them a year or so to seek a broader nuclear agreement with Iran while defusing the possibility that Israel might try to attack Iran’s nuclear installations before Iran gains more fuel and expertise.

A senior European official characterized the Iranian response as “basically a refusal.” The Iranians, he said, want to keep all of their lightly enriched uranium in the country until receiving fuel bought from the West for the reactor in Tehran.