VIENNA (Reuters) -- Iran's move to escalate uranium enrichment is unjustified because a draft nuclear supply deal it has snubbed contains guarantees for Tehran's benefit, according to a joint U.S.-Russian-French letter obtained by Reuters.
The letter to the UN nuclear watchdog was a response to Iran's launch last week of higher-grade enrichment -- raising suspicions of a quest for atomic bomb capability -- on grounds that world powers' terms for the deal were inadequate.
"[This] is wholly unjustified...If Iran goes forward with this escalation, it would raise new concerns about Iran's nuclear intentions," said the letter, dated February 12.
It said the UN proposal for Iran to swap enriched uranium for nuclear medicine fuel, which would defuse the risk of Tehran using the material for nuclear bombs, contained legal assurances it would be fulfilled, contrary to Iran's assertions.
Diplomats said the February 12 letter was leaked to refute Iranian statements this week that the powers had offered a new proposal to address Tehran's complaints about the plan, brokered by the International Atomic Energy Agency on October 21.
The letter was important also as a further signal of a hardening Russian line on Iran's nuclear defiance after years of buffering an important trade partner from stringent UN sanctions long sought by Western powers.
The Kremlin said today that Iran could face harsher measures if it failed to dispel fears abroad about its nuclear program.
The three powers' letter listed provisions that they said "provide assurances regarding our collective commitment" to carry out the deal, and Washington had offered "substantial political assurances" as well.
They said guarantees included the IAEA taking custody of Iran's nuclear material as part of the swap, a legally binding "project and supply" pact, and U.S.-Russian-French backing for IAEA technical aid to ensure the Tehran nuclear reactor that produces isotopes for cancer treatment operates safely.