Chevron said its Brazilian subsidiary requested the temporary shut-in of production at the Frade field as "a precautionary measure" following discovery of "a small new seep in the field."

The Frade field, located 370 kilometers (230 miles) off Rio de Janeiro state, currently produces roughly 60,000 barrels per day.

Chevron said it would conduct a comprehensive technical study and prepare a complementary study to better understand the geological features of the area, working with its partners and seeking necessary approvals from Brazil's National Petroleum Agency (ANP).

The US firm, which has a 51.74 percent operating interest in the Frade Field, said the suspension was endorsed by its Brazilian and Japanese partners in the project.

In November, Chevron was blamed for a major spill in the same area, with ANP calculating that some 3,000 barrels of crude were spilled.

Brazilian authorities as a result suspended all of Chevron's drilling operations and denied it access to huge new offshore fields, which ANP says have reserves that could surpass 100 billion barrels of high-quality recoverable oil.

Prosecutors also announced legal action against Chevron, its Brazilian unit and oil drilling contractor Transocean, seeking $11 billion over the November spill.

The top US Navy officer, Admiral Jonathan Greenert, told lawmakers the United States plans to send four minesweeping ships along with mine-hunting helicopters to the region -- bringing the total to eight for each type of asset.

"I wanted to be sure... that we are ready -- that our folks are proficient, they're confident and they're good at what they do in case called upon," Greenert told the Senate Armed Services Committee.

The move to boost US defenses in the region comes amid heightened tensions with Iran after it threatened to close the Strait of Hormuz, a key transit route for global oil supplies, in response to Western sanctions over Tehran's nuclear program.

The United States and Israel have said they would not accept a nuclear-armed Iran, despite Tehran's protests that its nuclear drive is for civilian purposes.

Four minesweeping ships are currently based in Bahrain, headquarters of the US Fifth Fleet. The US Navy has a total of 14 of these ships. The MH-53E Sea Dragon helicopters are equipped with sonars that can detect mines.

The US Navy also plans to improve submarine drones that can neutralize mines.

Tehran has an arsenal of about 2,000 marine mines that can be launched by a dozen of submarines or cruisers, according to experts.

In 1988, an Iranian mine damaged the USS Samuel B. Roberts frigate, causing $96 million in damage, according to the Dubai-based Institute for Near East & Gulf Military Analysis.