The state-run Russian company building Iran's nuclear power station says the launch date has been postponed because of Iran's payment delays.
Officials at Atomstroyexport say it is impossible to launch the reactor in September. They added there will be no delivery of nuclear fuel this month as earlier agreed.
Russia has accused Iran of missing payments on the nuclear plant. Iran has denied the claim.
Iranian and Russian officials met in Moscow last week, but failed to solve their financial dispute.
Russia's Interfax news agency quotes a Russian foreign ministry spokesman, Andre Krivtsov, as saying Moscow hopes the two countries will find a mutual solution to their funding problem.
The United Nations Security Council has expressed concern that Iran could use uranium enrichment technology to develop nuclear weapons.
Iran says its nuclear program is only for energy purposes.
Some information for this report was provided by AFP and Reuters.
