Mitt Romney, the US Republican presidential candidate, is to reveal his choice for running mate in the November election on Saturday, his campaign says.

The vice-presidential candidate will be named at an event on a former warship, the USS Wisconsin, in Norfolk, Virginia, at 09:00 EDT.

Unconfirmed US media reports say Mitt Romney has decided on Wisconsin congressman Paul Ryan.

But the campaign has made no official comment on the candidate’s identity.

Mitt Romney is challenging President Barack Obama in the 6 November vote.

Analysts say Mitt Romney will be hoping to wrest back momentum in the campaign after a series of pro-Obama campaign ads attacking his record.

The former governor of Massachusetts is set to begin a four-day bus tour through key battleground states.

The trip campaign will visit the states of Virginia, North Carolina and Florida before finishing in Ohio.

Unconfirmed US media reports say Mitt Romney has decided on Wisconsin congressman Paul Ryan as running mate for November election

In particular, Mitt Romney will seek to fight back against the Democrats’ push to portray him as upper-class and out-of-touch with ordinary Americans, observers say.

Recent opinion polls suggest a close race between the two men, with Barack Obama tending to have a slight lead in most surveys.

The vice-presidential announcement is expected to be made during a tour of the USS Wisconsin, a decommissioned battleship docked in Norfolk’s Nauticus Museum.

Dating back to the World War II-era, the vessel also saw service during Operation Desert Storm in 1991.

Several US media reports said all the signs were pointing to 42-year-old Paul Ryan as the leading contender to be Mitt Romney’s running mate.

A Republican official, speaking on condition of anonymity, also told reporters that Paul Ryan would be chosen.

If Paul Ryan is confirmed as Mitt Romney’s running mate, it would be a bold and ideological choice for a candidate who has been fairly cautious so far.

As chairman of the Budget committee in the Republican-controlled House of Representatives, Paul Ryan is seen as likely to add electoral firepower on what are expected to be the key election issues – jobs, the economy and the budget deficit.

He is also a staunch conservative who could enthuse the Republican base, and counteract some conservatives’ skepticism about Mitt Romney’s political past as governor of the traditionally liberal state of Massachusetts.

Other Republicans mentioned as being on Mitt Romney’s shortlist include Ohio representative Rob Portman, 56, and former Minnesota governor Tim Pawlenty, 51.

Rob Portman is seen as likely to help Mitt Romney gain votes in the important swing state of Ohio, while Tim Pawlenty could improve Romney’s appeal to working-class voters.

In a little over two weeks’ time, Mitt Romney will be formally confirmed as candidate at the Republican Party convention in Tampa, Florida.

His bitter rival in the primaries, Rick Santorum, will be a speaker at the convention, it was announced earlier in the week.

Paul Ryan profile:

• Aged 42, Paul Ryan was elected to the House of Representatives at 28 and is currently the Republican congressman for Wisconsin

• Seen as young and dynamic and a rising star in the Republican party

• Chairs the House Budget committee and has worked on reshaping federal budget

• A staunch conservative, he is best known for his proposals for large cuts in spending and taxes, which have proved popular with grassroots Republicans