Updated

Iran is helping Venezuela to detect uranium deposits and initial evaluations suggest reserves are significant, the South American government said Friday — the same day world leaders criticized the Islamic republic of secretly building a uranium-enrichment plant that could be used to make an atomic bomb.

Mining Minister Rodolfo Sanz said Iran has been assisting Venezuela with geophysical survey flights and geochemical analysis of the deposits, and that evaluations "indicate the existence of uranium in western parts of the country and in Santa Elena de Uairen," in southeastern Bolivar state.

"We could have important reserves of uranium," Sanz told reporters upon arrival on Venezuela's Margarita Island for a weekend Africa-South America summit. He added that efforts to certify the reserves could begin within the next three years.

The announcement came as revelations that Iran has secretly been building a uranium-enrichment plant provoke concerns among countries including the U.S., Russia, France, Britain, Germany and China.

On Friday, Russian President Dmitry Medvedev urged Iran in a statement to prove it is not seeking to develop atomic weapons, saying the undeclared construction of an enrichment facility flies in the face of U.N. Security Council demands for Iran to stop uranium enrichment at its only declared facility.

Iran is under three sets of Security Council sanctions for refusing to freeze enrichment at what had been its single publicly known enrichment plant, which is being monitored by the International Atomic Energy Agency.

U.S. State Department spokesman Ian Kelly said recently that U.S. officials also have "concerns" about a possible transfer of nuclear materials between Iran and Venezuela.

But analysts say Iran, which has significant uranium deposits, currently has no need to import uranium, although those deposits may not be enough to sustain its future enrichment goals.

Sanz dismissed suggestions that Venezuela could aid Iran with its nuclear program, saying Venezuela is only aiming to develop nuclear energy for peaceful purposes. Chavez has repeatedly said that all countries should end their nuclear-weapons programs, while insisting that Iran and Venezuela have a "sovereign right" to pursue peaceful nuclear ambitions.

Michael Shifter of the Inter-American Dialogue in Washington said that regardless of whether the uranium exploration efforts lead to nuclear cooperation, they are going to cause "a serious problem in the relationship" between Caracas and Washington.

Chavez's government has "clearly announced they're sort of beginning down this road," Shifter said. "It's going to be very difficult for the U.S. to really pursue any cooperation with Caracas on other issues because this is going to top everything else."

Chavez's project remains in its planning stages and still faces a host of practical hurdles, likely requiring billions of dollars, as well as technology and expertise that Venezuela lacks. Russia has offered to help bridge that gap, and Chavez has announced that the two countries have created an atomic energy commission.

But Sergei Novikov, a spokesman for Russian state nuclear agency Rosatom, has said there are no concrete projects and that any joint work on mining deposits of uranium or the radioactive metal thorium would have to wait until Venezuela decides whether it wants Russian help exploring them and, if so, create a joint venture for the purpose.

Both Chavez and Iranian President Mahmoud Ahmadinejad are well-known for their anti-U.S. rhetoric, and have forged ties in everything from finance to factories, provoking concerns in Washington. Iran now manufactures cars, tractors and bicycles in Venezuela.

Earlier this month, Chavez sealed a deal to export 20,000 barrels of gasoline daily to Iran, giving Tehran a cushion if the West carries out threats of fuel sanctions over Iran's nuclear program.