Barack Obama accused John McCain of "smear tactics" and said he was not paying enough attention to the economic crisis that has been gripping the US.

John McCain said Mr Obama was "lying" about his ties to the home loan industry and asked what his rival had ever accomplished in government.

The campaign tone has turned nasty as polls show Mr Obama widening his lead.

Polling numbers

The latest Gallup daily tracking poll puts Senator Obama at 50% and Senator McCain at 42%, while a new CNN poll put Mr Obama ahead by 53% to 45%.

Mr Obama, the Democratic candidate, is still gaining in some of the key swing states as well. A new Washington Post poll puts him 6% ahead of Mr McCain in Ohio, a state the Republican candidate must take if he is to win the presidency.

The poll also showed that the Obama camp had a stronger organisation on the ground, with 43% of potential voters having been contacted by Democratic supporters, while only 33% had heard from McCain supporters.

With voter registration having closed in many key states on Monday, the evidence suggests that the majority of the four million new voters added to the electoral roles are registering as Democrats - for example, in Florida, it is by a two to one majority.

Town Hall debate

The second presidential debate is generating intense interest among the public.

Barack Obama is fighting back over attacks on his character

More than six million people have e-mailed questions to the moderator, NBC news presenter Tom Brokaw, who will preside over the town hall-style debate in Nashville, Tennessee.

He will select only six or seven e-mailed questions, as well around a dozen from the studio audience of 80 uncommitted voters.

Mr McCain, who is widely viewed as having lost the first debate, has vowed to take the gloves off for this encounter.

Mr Obama, meanwhile, promised to fight back.

"We don't throw the first punch, but we'll throw the last," he told a syndicated radio show.

Fresh accusations

In recent days both camps have launched fresh accusations questioning the character of their opponent.

Mr McCain's running mate Sarah Palin posed further questions about Mr Obama's "truthfulness and judgement."

Sarah Palin has been attacking Senator Obama's character

Governor Palin had accused Mr Obama of "palling around" with a "domestic terrorist" - Bill Ayers.

He belonged to the US militant group Weather Underground, which opposed the Vietnam War in the 1960s.

Mr Obama once served on a charity board with Mr Ayers but has denounced his radical past.

In an interview with the New York Times newspaper on Monday, Mrs Palin also suggested that voters should pay more attention to Mr Obama's relationship with his former church pastor, the Reverend Jeremiah Wright.

"I don't know why that association isn't discussed more, because those were appalling things that that pastor had said about our great country," she said.

Mr McCain had previously indicated that he did not want Rev Wright's inflammatory sermons, which Mr Obama has repudiated, to form part of his campaign.

Judgement claim

Meanwhile, the Obama campaign has been highlighting Mr McCain's involvement in a financial scandal 20 years ago.

At the weekend, the Obama campaign e-mailed supporters an internet video about Mr McCain's connections to Arizona tycoon Charles Keating, who was convicted of securities fraud after his savings and loan bank collapsed.

Mr McCain was one of five senators - known as the Keating Five - to be investigated by a Senate ethics panel over their intervention with banking regulators on behalf of Keating.

He was found to be less involved with Keating than the other senators but was criticised for "poor judgement".

Mr McCain has himself described the affair as "the worst mistake of my life", and one which led him to sponsor legislation on campaign finance reform.

BBC