The FBI is looking into possible insider trading in the options of ketchup maker HJ Heinz before its blockbuster deal last week to be acquired by Warren Buffett and Brazil's 3G Capital, a bureau spokesman has said.

Buffett's Berkshire Hathaway and 3G said last Thursday that they would buy Heinz for $23bn in cash.

Almost immediately, options market players noted there had been extremely unusual activity the day before the deal was announced.

"The FBI is aware of the trading anomalies the day before Heinz' announcement," a spokesman for the Federal Bureau of Investigation said on Tuesday. "The FBI is consulting with the [US] SEC [Securities and Exchange Commission] to determine if a crime was committed."

On Friday, the SEC filed a suit against unknown traders who it said used a Goldman Sachs account in Switzerland to trade on purported inside knowledge of the transaction.

A spokeswoman for the investor group declined to comment on the FBI's involvement.

A spokesperson for Goldman Sachs said the bank is cooperating with authorities' investigations.

Swiss authorities have already said they have not been asked to help with the US probe.

The SEC enforcement action marked the second time in six months regulators have taken aim at alleged insider trading in a deal involving 3G.

The first instance, last September, involved a stockbroker trading on inside information related to 3G's 2010 purchase of Burger King.