Authorities in Bolivia backpedaled Tuesday after claiming that they had seized nearly two tons of uranium in central La Paz, saying instead they had found rocks with possible traces of the substance.

"We assume that uranium exists in these materials but this should be clarified," Interior Minister Carlos Romero said at a news conference. "It's possible that uranium is disseminated on this solid material."

Romero said the find was moved to the outskirts of La Paz, where it will be analyzed. Four people have been arrested, he added.

Earlier Tuesday, Deputy Interior Minister Jorge Perez had told reporters that nearly two tons of uranium had been found in a garage on the ground floor of a building in central La Paz, not far from the US and Brazilian embassies.

Experts were to quickly examine the material, which the deputy minister said appeared to have a "high level of radioactivity." Perez did not explain how the discovery was made, or the specific nature of the uranium.

Perez had also said the material, found in heavy plastic bags as a result of a six-week investigation, was likely destined for Chile.