White House hopeful Barack Obama has a narrow three-point lead over his Republican rival John McCain less than a month before the election, according to the latest poll.

The results of the poll were published as Mr Obama and Mr McCain prepare for the second of their three scheduled debates which takes place in Nashville, Tennessee.

The McCain campaign has unleashed a volley of attacks on Mr Obama in the last few days as his advisers signaled they wanted to turn the debate away from the economy.

Mr McCain and running mate Sarah Palin have tried to turn the campaign focus back to Mr Obama and his associations with figures like former 1960s radical William Ayers and his former minister, the Rev Jeremiah Wright.

That drew a counter-attack from Mr Obama, who raised questions about Mr McCain's relationship with Charles Keating, a central figure in the US savings and loan scandal in the late 1980s and early 1990s that cost taxpayers billions of dollars.

Mr McCain's aggressive tone and his rival's sharp responses have raised expectations for an explosive debate.

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