Comcast Corp's NBC Universal purchase will be delayed until at least next month, with federal regulators taking longer than the companies had hoped to sort through the deal.

NBC Universal Chief Executive Jeff Zucker, who will leave the company once the deal is completed, circulated a memo to staff on Wednesday saying: "We have made substantial progress this month with both the FCC and the Department of Justice, and expect that we will get a 'green light' in January."

Comcast, the largest U.S. cable company, confirmed the delay. It had initially hoped to close the transaction this year.

"Because of the lead time required to prepare for a close, it now appears that we will not be able to close the transaction with GE relating to NBC Universal by year-end," a spokeswoman said in a statement. "We have notified our transition teams that there will not be a December 31 closing."

Comcast revealed its bid to buy a controlling stake in NBC Universal from General Electric Co more than a year ago to create a $30 billion business including broadcast, cable networks, movie studios and theme parks.

Regulators from the U.S. Department of Justice and the Federal Communications Commission have been examining several areas of contention, including online video, program access and program carriage, sources have said.

Regulators are concerned that Comcast could be in a position to stifle the fledgling online video market if it assumed partial control of Hulu, a joint venture of NBC Universal, News Corp and Walt Disney Co.

They also want to prevent Comcast from anti-competitive discrimination with the wealth of programing and networks it would own once the deal closed, including leading networks like USA, Bravo and MSNBC.

Under terms of the deal, Comcast is buying a controlling 51 percent stake from GE.