Barack Obama has caused a storm by attacking Republican vice presidential nominee Sarah Palin.

The Democratic presidential nominee said: "You can put lipstick on a pig, but it's still a pig."

The comment was a barbed reference to Ms Palin's description of herself as "a pit bull in lipstick" in her acceptance speech last week.

Mr Obama, watched by millions of viewers on CNN, continued: "You can wrap an old fish in a piece of paper called change. It's still going to stink after eight years."

His comments were immediately criticised by Republicans.

McCain's campaign called the comments "offensive and disgraceful" and said Obama owes Palin an apology.

Obama's campaign said he wasn't referring to Palin and said the Republican camp was engaging in a "pathetic attempt to play the gender card."

Mr Obama told an audience in Virginia that his Republican opponent John McCain says he'll change Washington, but he's just like President George W. Bush.