McCain ad says Obama 'too risky'

Republican presidential hopeful John McCain has ratcheted up his assault on his Democratic rival's character, with a new advert branding him "too risky".

The ad accuses Barack Obama of hiding ties to Bill Ayers, an ex-member of former militant group, the Weathermen.

Mr Obama has insisted he is not close to Mr Ayers. A spokesman said the ad was a "desperate and dishonest" attack.