Moscow ? The Iranian government has been slow in payments for a Russian-built nuclear power plant and the reactor’s launch could be delayed, Russian officials said Monday. A top Iranian nuclear official swiftly denied payments had been disrupted and accused Russia of trying to prolong the launch.

The conflicting allegations were the latest sign of financial disputes dogging the deal at the center of Russia’s nuclear cooperation with Iran.

Iran broke the schedule of payments this year under the $1 billion contract to build the Bushehr nuclear plant, said a government official, who asked not be named because he was not authorized to speak to the media. He said the Iranians blamed the delay on the need to switch payments from dollars to euros.

Last year, Russia agreed to ship fuel to the plant in southern Iran by this March and launch the facility in September, with electricity generation to start by November.

But Mohammad Saeedi, the deputy head of the Atomic Energy Organization of Iran, denied that Iran had been late making payments.