Iranians will hear "Good news" on their country's nuclear program on Tuesday night, President Mahmoud Ahmadinejad was quoted as saying by the official IRNA news agency.
The news is widely expected in Iranian media to be the announcement that Iran has enriched uranium to the 3.5 percent level needed to fuel nuclear power stations like the one it is building at the Gulf port of Bushehr.
Such an announcement would be a big setback to U.N. efforts to get Iran to suspend its uranium enrichment work, as it has done before.
"After hearing all the good news tomorrow (Tuesday) night, Iranians should prostrate themselves before almighty God," Ahmadinejad said in the northeastern city of Mashhad on Monday night.
Iran has been referred to the U.N. Security Council after failing to convince the international community that its nuclear activities are aimed a producing only nuclear power, and not weapons.
The world body has demanded Iran suspend its uranium enrichment work and on March 29 asked the Vienna-based International Atomic Energy Agency (IAEA) to report on Tehran's compliance in 30 days.
IAEA Chief Mohamed ElBaradei is expected to visit Iran this week and any announcement of advances in uranium enrichment work by Iran could cast an embarrassing cloud over his visit.
Iranian nuclear officials have previously said enriching uranium to 3.5 percent would require the operation of 164 centrifuges, which spin it at supersonic speeds to increase the concentration of uranium's most radioactive isotope.
The level of enrichment needed for warheads is far higher, but analysts says it will be unacceptable to many in Washington that even low-level enrichment is under way.
"After the good nuclear news, the psychological war against us will start," Lawmaker Gholamreza Mesbahi-Moghaddam told a parliament session on Tuesday.
"I can say there will be international media campaign against us in the next days because of the news the president will announce."