US regulators investigating potential insider trading in Thursday's $23bn takeover of Heinz have asked a court to freeze the Swiss bank accounts of unnamed traders who may have speculated on the deal before its announcement.

Less than 40 hours after Berkshire Hathaway and 3G Capital announced they were together buying Heinz, the Securities and Exchange Commission said it was seeking an emergency court order freezing the Zurich-based assets of the traders and prohibiting them from destroying any evidence. The SEC said it was chasing "highly suspicious options trading activity" that may have earned the traders as much as $1.7m.

The SEC alleges that the traders knew details of the Heinz acquisition before they had been made public. "The SEC alleges that the unknown traders were in possession of material non-public information about the impending acquisition when they purchased out-of-the-money Heinz call options the day before the announcement."

On Wall Street, the only surprise in the SEC's announcement was its speed. The issue of insider trading was widely discussed among investors interested in Heinz after the deal. Immediately after the deal was announced, savvy investors noticed that something was odd about the Heinz option contracts.

Options are a way for investors to bet on the future price of the stock. Traders noticed that the afternoon before the deal was announced, an unusual number of Heinz options contracts – 2,593, to be exact – were bought, particularly betting that the stock would be worth at least $65 in June. Previously, Heinz stock had not been worth more than around $60 in over a year.

Traders familiar with Heinz options said the contracts were bought starting at 2.22 pm on February 13, the day before the deal, and that they were bought in small lots. If that proves to be the case, the small lots may have been designed to evade attention.

The court order will force the traders to appear in court to explain why they were trading in Heinz options the day before the deal was announced, said Sanjay Wadhwa of the SEC's New York Regional Office. He commented on "the obvious logistical challenges of investigating trades involving offshore accounts." It is not yet clear how the SEC traced the trades overseas so quickly.

The SEC described its method in tracing the unusual trading activity. Heinz has not been popular with speculators. Its stock and options were very stable and showed very little action for months beforehand, which made the unusual spike all the more incongruous.

"The timing and size of the trades were highly suspicious, because the account through which the traders purchased the options had no history of trading Heinz securities in the last six months," the SEC said in a statement. "Overall trading activity in Heinz call options several days before the announcement had been minimal."

One trader who makes bets on mergers said the SEC discovered the unnamed traders because the options trading was "obvious" and "stupid."