Democrat Barack Obama on Thursday did not rule out selecting rival Hillary Clinton as his vice-presidential running mate if he ultimately defeats her in a race in which he has an almost insurmountable lead.

"There's no doubt that she's qualified to be vice-president, there's no doubt she's qualified to be president," Obama told NBC News.

In a CNN interview, he said he had not wrapped up the Democratic presidential nomination, but when he does, he will start going through the process of selecting a running mate.