RICHMOND, Va. — Presumptive Republican presidential nominee Mitt Romney will announce his running mate at the beginning of a four-day, four-state bus tour in Norfolk, Va., on Saturday morning, his campaign announced in a statement late Friday night.

Romney called several of the Republicans on his vice presidential shortlist on Friday evening to tell them he has selected a running mate and to thank them for assisting with his campaign, a Republican familiar with the calls told CNN. Romney did not indicate on the calls who he had selected as his running mate, according to the source.

Three Republicans close to the Romney campaign told CNN that key staffers have been told to prepare for the rollout on Saturday morning, when Romney tours the U.S.S. Wisconsin, a museum battleship at the National Maritime Center in Norfolk.

Communications staffers for the Romney campaign have been ordered to report to their Boston headquarters at 8 a.m. Saturday morning, an unusual directive for a weekend, a Republican familiar with the plans told CNN.

There were other signals that Romney-world was ramping up for a splashy weekend: Much of the Romney high command flew with the candidate from Boston to Norfolk on Friday afternoon, including Beth Myers, the adviser tasked with running the vice presidential search process, and Will Ritter, the campaign’s director of advance who rarely leaves his spacious corner office in Boston’s North End.

Ann Romney, the candidate’s wife, also landed in Norfolk after her trip to the Olympic Games in London.

The bus tour itself has also been driving vice presidential chatter since its itinerary was first revealed by CNN early last week.

The campaign swing will take Romney through major media markets in four battleground states: Virginia, North Carolina, Florida and Ohio.

Romney will be joined at various stops by bold-faced names in Republican politics; Virginia Gov. Bob McDonnell, one potential running mate, and House Majority Leader Eric Cantor, a Richmond native, were set to join Romney at stops in the commonwealth on Saturday.

The appearance of a private plane that had traveled from Boston to Janesville, Wisconsin – the home of Rep. Paul Ryan, a top contender for Romney’s number two – added fuel to the Ryan rumor mill after the plane’s itinerary was reported by The National Review just before 6 p.m. on the east coast.

The Ryan talk on Friday evening seemed to confirm late speculation that the prospects for the two supposed VP frontrunners, Ohio Sen. Rob Portman and former Minnesota Gov. Tim Pawlenty, have faded in recent days.

The Friday buzz instead centered on Ryan and Florida Sen. Marco Rubio, who is on vacation with his family and whose whereabouts are known only by a handful of advisers.

Rubio has long been dismissed as a serious contender by Beltway insiders thanks to his relative lack of experience, his controversial use of a Republican Party of Florida credit card and his friendship with scandal-tainted Rep. David Rivera.

But his stock has risen in recent weeks, knowledgeable Republicans said, especially with internal Romney polling showing the campaign with abysmal numbers among Hispanic voters in Florida.

The Romney camp has also come under considerable pressure from the conservative pundit class to pick a running mate more “bold” than Portman or Pawlenty.

The Friday evening rumor mill sent political reporters scrambling, with some even dialing Obama campaign strategists in Chicago in a desperate but fruitless search for more clues.

And yet many Republicans who spoke to CNN — all of them granted anonymity to speak freely without angering Romney officials in Boston — wondered why Romney would announce the pick on a weekend when millions of potential voters are likely to be distracted by the Olympics, PGA golf, late season baseball and the box office release of the latest Bourne thriller.

“This is probably just the Romney campaign jerking with the press,” said one Republican operative close to one of Romney’s potential running mates, referring to the private jet in Wisconsin.

Many rank-and-file Romney staffers contacted by CNN remained clueless about plans for VP rollout, but admitted that it would only take a late night phone call and a few hours to fly Romney’s pick into Virginia from Florida, New Hampshire, Ohio or elsewhere early on Saturday morning.

Aides to several Republicans on the vice presidential shortlist said their bosses had not been contacted by Romney as of Friday evening.