Tehran, Iran ? Iran accepted the general framework of a U.N.-draft nuclear deal Tuesday, but said it would seek “important changes” that could test the willingness of world powers to make concessions in exchange for a pact to rein in Tehran’s ability to make atomic warheads.

It was unclear how far Iran would push for those changes. Already, Iran has raised a potential roadblock: It wants a step-by-step approach to send low-enriched uranium stockpile out of the country rather than the big single shipment called for under U.N. provisions.

Western powers say it’s critical for Iran to send out at least 70 percent of its uranium store in one load to eliminate — at least temporarily — its options to make a nuclear weapon. A significantly lower amount or gradual shipments by Iran could jeopardize a key part of the proposal, which was reached after talks last week that included the United States.

For the moment, Iran has signaled that it agrees to the plan’s basic premise: sending its low-enriched uranium to Russia for further processing. The announcement on state media marked a major step for Iran, which has been reluctant to give up full control of the nuclear enrichment cycle.

Tehran’s ideas

Tehran still may be a long way from finalizing a deal. Western leaders were anticipating additional caveats by the Islamic republic, which is conducting its negotiations in public with a trickle of hints and statements on state-run media.

Iran’s state-run Arabic-language channel Al-Alam cited an unidentified official as saying Iran will officially reply on the deal within 48 hours — or Thursday in Tehran. Other reports said it could Friday.

Iran “will agree to the general framework” of the plan “with a request for important changes,” the official said.

French Foreign Minister Bernard Kouchner expressed exasperation, saying Tehran is trying to have the proposal “thoroughly reworked.”

“It cannot take forever. We wait for answers,” he said in Luxembourg.

The plan was formalized by the United Nations last week after talks between Iran and the United States, Russia and France. It calls for Iran to ship 70 percent of its enriched uranium abroad for further enrichment. The U.S. and its allies back the deal because it would at least temporarily leave Iran’s uranium stockpiles too low to build a nuclear weapon. Iran denies any intention to develop a bomb.

Another Iranian state channel, Press TV, said Tehran opposes sending the entire shipment abroad at once, suggesting it wants to do it in stages.

The head of Iran’s Foreign Policy and National Security Commission, Alaeddin Boroujerdi, was quoted by Iran’s semiofficial ILNA news agency as sketching out a scenario in which Iran would send out portions of its low-enriched uranium stockpiles only after it receives a batch of reactor-ready rods.

Iran has also given hints that it may want to send less than 70 percent of its stockpiles abroad. On Monday, Iranian Foreign Minister Manouchehr Mottaki said Iran might agree to “deliver part of (the low-enriched uranium) fuel which we currently don’t need.”

A French diplomat said he expects Iran will seek to dramatically reduce the amount of uranium it would ship out of the country. The diplomat in Paris spoke on condition of anonymity because of the sensitivity of the situation.

The European Union’s foreign policy chief, Javier Solana, who is also negotiating with the Iranians, said: “The deal was a good deal, and I don’t think it requires fundamental changes.”

Enrichment process

In the enrichment process, uranium purified to a low level — 5 percent or below — is used as fuel for a nuclear reactor, and to a somewhat higher level — around 20 percent — it can power a research reactor. The United States and its allies fear Iran secretly intends to further enrich its low-enriched uranium to more than 90 percent purity, the level needed to build a bomb. Iran contends its program is intended only to generate electricity.

Around 2,200 pounds of low-enriched uranium is needed to produce enough weapons-grade uranium for a single nuclear warhead, according to experts. Iran is believed to have well over that amount of low-enriched uranium in its stockpiles.

The U.N. plan would require Iran to send 2,420 pounds to Russia in one batch by the end of the year to be enriched further. It would then be sent to France to be made into isotopes for use in a Tehran research reactor. Doing so would put Iran well below the quantity needed for a bomb — for a period, anyway, until it enriches more uranium in its facility to refill its stockpiles.

Since the agreement was first discussed in Geneva earlier this month between Tehran and six world powers, diplomats from some of the countries involved have insisted the uranium shipment would have to be in one batch to be acceptable, or in two, at most, with little time elapsed in between.