Russian Defense Minister Sergei Ivanov said Friday that talks with an Iranian delegation next week on a Russian uranium enrichment offer will be difficult and their outcome impossible to predict, news reports said.

"I don't know how the talks will end, but they won't be easy," Ivanov said, according to the ITAR-Tass news agency. "The situation around the Iranian nuclear program is quite difficult."

Russia's proposal to host the Iranian uranium enrichment program has become the focus of international efforts to defuse tensions over Tehran's nuclear bid.

An Iranian delegation had been expected to visit Moscow on Thursday to discuss the Russian proposal, but Tehran put off the talks until Monday.

The Russian offer has been backed by the United States and the European Union as a way to provide international oversight of Iran's nuclear activities and ease international suspicions that Tehran aims to use its nuclear program to produce weapons. Iran's lukewarm attitude has drawn suspicions that it was merely using the proposal to stall for time.

Russian Foreign Minister Sergey Lavrov warned Tehran this week that Russia's enrichment offer was contingent on Iran re-imposing a freeze on enrichment at home.

A senior Russian diplomat said Friday that Moscow would "persistently urge" Iran to return to the enrichment moratorium it broke last month, the ITAR-Tass news agency reported. The diplomat said there was firm agreement that the Iranian delegation would arrive Monday, but he did not agree to be identified — apparently reflecting concerns that the Iranians again might call off the trip, denting Russia's prestige.

Iranian Ambassador to Moscow Gholamreza Ansari said Thursday that the delegation would "definitely" come Monday.