Argentine police are investigating reports that a small plane sprayed white powder over suburb south of Buenos Aires.
Emergency workers and firemen took samples of the powder found in Lomas de Zamora, a neighborhood some 19 miles south of the capital, and have sent them to be analyzed.
Residents said a small plane flew over the area last night and sprayed a "suspicious" substance over some six blocks, a police spokesman said.
"Some inhabitants saw white powder in some areas and they linked it to a plane that had passed overhead. They did not see if the plane had actually released the substance," the police spokesman said.
Fears grew in Argentina after a US letter sent to an Argentine woman tested positive for anthrax last week. Later reports that it was an unusual harmless strain of the bacteria have just added to confusion.
Argentines, worried that their country could be target for attacks given it is a strong US ally in Latin America, are sending hundred of letters to heath authorities for testing.