U.S. national security adviser H.R. McMaster is most likely the next official to leave the Trump administration following a string of firings and resignations, according to a betting website that put the odds against him staying, at 3-2.

President Donald Trump's record-setting personnel turnover inspired Costa Rica-based BetDSI to begin taking bets on White House departures and it said the chances for any particular staff member remaining employed in the White House are not high.

"Due to the ongoing turnover we've seen thus far in the Trump Administration, no member on this list can feel particularly safe in their position," BetDSI said in a statement on the 24 Trump officials it gave odds for.

Turnover among White House senior staff during Trump's first year was at least twice as high as that of any of the five past presidencies, according to Brookings Institute research.

After firing U.S. Secretary of State Rex Tillerson on Tuesday, the president has been talking to confidants about replacing McMaster and Veterans Affairs Secretary David Shulkin, sources familiar with the conversations said.

The likelihood that Shulkin will be removed within days are so high that BetDSI did not include him on its odds list.

Most likely to exit, after McMaster, were Attorney General Jeff Sessions and press secretary Sarah Huckabee Sanders, with odds of 7-4 and 6-1.

Among staffers whose jobs appeared most secure are Vice President Mike Pence at 50-1 and Small Business Administration chief Linda McMahon with the same odds.

Such is the concern among White House employees about job security that chief of staff John Kelly on Friday assured Trump aides that no immediate personnel changes were in the works, Sanders told reporters on Friday.