After a week of rumours about his position as the CEO of the IZOD IndyCar Series, Randy Bernard has officially stepped down following an emergency teleconference of the board of directors of the Indianapolis Motor Speedway Corporation on Sunday afternoon.

IMSC president Jeff Belskus will take over as CEO on an interim basis. Previously announced plans for a 19-race season in 2013 will continue uninterrupted.

"We are very grateful for the tireless effort that Randy has invested into learning, understanding and working to grow the IndyCar Series over the last three racing seasons," said Belskus.

"As both Randy and our organisation have reflected on the past season and as we look toward the opportunities ahead and how to best take advantage of them, we agreed that the timing was right to pursue separate paths," he added.

A former CEO of the Professional Bull Riders series, Bernard joined IndyCar in March 2010 on a five-year contract and has said repeatedly that he would not leave the series prematurely before the end of that period unless asked to do so by the owners.

However, speculation about his position reached fever pitch on Friday with reports in the Indianapolis Business Journal quoting anonymous "sources familiar with the situation" to assert that Bernard had already been fired by the series owners on Thursday and was currently negotiating a severance package.

The reports were strongly refuted by a IMSC spokesperson on Friday, who said: "Randy has not been terminated and his employment status is the same as it was last week and last month."

Doug Boles had added: "At this point, Randy is not fired. That is the case at the moment and in the future." That future turned out to be a little over 48 hours.

Officially, Sunday's emergency board telemeeting was only called after Friday's IBJ story sparked a media storm that many on the board felt made Bernard's position as CEO untenable and which could only be resolved by a "mutual separation."

In the official statement confirming his exit, Bernard is quoted as saying he is confident he leaves IndyCar in a better condition than he found it when he took on the role three years ago.

"I have enjoyed the opportunity to work with the entire IndyCar community, its teams, drivers, loyal partners and fans," said Bernard said. "The last three years have produced some exciting, and some difficult, times.

"I am proud of what everyone at IndyCar has been able to accomplish since I came on board," he added. "We have created a foundation for IndyCar that positions it to grow over the next several years."

Bernard also thanked the Hulman-George family that owns and runs the Indianapolis Motor Speedway for "giving me the opportunity and privilege to work with the organization and to help set a course and direction for IndyCar."

Bernard indicated that he would maintain an advisory capacity with the series that would allow him to continue to provide input to IndyCar in the future. "I have developed a passion for the sport of IndyCar, and I look forward to being involved at a strategic level as an advisor to the IndyCar leadership.

"As IndyCar fans, we need to unify behind the sport in order to move it to the next level, and I look forward to providing input and being part of that unified voice along the way," he added.

Interim CEO Jeff Belskus thanked Bernard for piloting the series through some difficult time, which included the introduction of a brand new chassis and engine technical specification for the first time in nine years.

Belskus has previously served as interim CEO of IndyCar from July 2009 until Bernard's appointment in March 2010. He will continue to serve in his present roles as CEO and president of the International Motor Speedway.

Belskus said that no specific timeline for finding a permanent replacement had yet been agreed, and would likely be tied into an overall review of the leadership of the series. That review would be supported by global business management firm The Boston Consulting Group and would include consultation with existing IndyCar stakeholders.

He reiterated that Bernard's departure and the management review did not mean that the series was about to be sold to an investment group led by former IMS and IndyCar president Tony George, who is leading a takeover bid that involves a number of current team owners.

"Once again, IndyCar is not for sale, and the organization remains completely committed to owning and operating IndyCar," he said.

The official statement announcing Bernard's departure did not state any reasons at all for the move, but the decision by the board to accept Bernard's resignation as CEO is believed to be motivated by a sharp rise in losses by the series in 2012.

IBJ's report on Friday said that these had spiked to over $7m, partly due to the last-minute cancellation of a lucrative race scheduled for China over the summer. That had been expected to bring in around $9m in sanctioning fees until the local authorities pulled out of the arrangement.

While popular with fans, Bernard's decision to stand up to team owners over key decisions has left him increasingly at odds with them in recent months. The cost of replacement parts for the new Dallara chassis was also a major bone of contention between the owners and Bernard's management team. Rumours that some of the car owners were actively lobbying the board of owners to have Bernard removed surfaced in May in the run-up to the Indianapolis 500, and Bernard controversially went public to confirm the rumours via Twitter.

After that the speculation died down, but since the end of the 2012 season last month the rumours have returned up and gathered even more momentum. The news that a formal buyout bid had been presented to the board by Tony George only escalated the furore still further.

Tony George is a controversial figure for many fans of US open sport, who still hold him responsible for the schism in US open wheel racing that resulted when he set up the Indy Racing League in the 1990s to break away from CART sanctioning. It was a split that wasn't resolved until the reunification of IRL with CART's rump Champ Car World Series in 2008, by which time the sport's popularity had nosedived in comparison with NASCAR.

Even if the mooted buyout was to go through, George is unlikely to want to take over again as CEO. The investment group behind the takeover bid is said to have the involvement of motorsports marketer Zak Brown, who is seen as the leading replacement for Bernard as CEO.

Other suggested candidates are Andretti Autosport's executive vice president and chief operating officer John Lopes, or Daytona International Speedway's president Joie Chitwood III, a former chief operating officer at IMS for seven years when George was the CEO there.