Brazilian oil giant Petrobras has reported "drops of oil on the ocean floor" near a Chevron-operated field that leaked some 2,400 barrels in November, sparking a major legal battle.

The oil was found during an inspection on Sunday in the Roncador field, some 120 kilometers (75 miles) off the coast of Rio de Janeiro and around 500 meters (1,600 feet) from the Chevron-run Frade field, Petrobras said late Monday.

"No oil slick was found on the surface and a sample of the oil droplets was taken for analysis and to determine its origin. Competent authorities have been informed of the situation," it said in a statement.

Brazil's National Petroleum Agency (ANP) said it had been "informed of the spill" following inspections by a remotely operated undersea vehicle.

Last month an oil spill was detected at a depth of 1,300 meters (4,200 feet) in the Frade field not far from the site of the bigger spill that occurred in November.

State prosecutors have filed legal action against Chevron and the oil-drilling contractor Transocean over the November incident, seeking $11 billion for what they have called "immeasurable" environmental damage.

Police and prosecutors alleged last month that the Frade spill was caused by an error on Chevron's part.

The US oil giant has denied the charges as "outrageous and without merit" and has vowed to challenge them in court.