Mitt Romney to announce candidate for vice-president

US Republican presidential candidate Mitt Romney 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 (13:00 GMT).

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

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

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

Analysts say Mr 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.

Paul Ryan is passionate about ideas, and if he is chosen, it may elevate a campaign which has looked dirty and petty in recent days”

In particular, Mr 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 Mr 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 Mr Ryan as the leading contender to be Mr Romney's running mate.

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

The BBC's North American editor, Mark Mardell, says that if Mr Ryan is confirmed as Mr 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, Mr 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' scepticism about Mr Romney's political past as governor of the traditionally liberal state of Massachusetts.

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

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

In a little over two weeks' time, Mr 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.