Ben Affleck has compared US Republican presidential candidate Mitt Romney to past campaign losers Al Gore, Michael Dukakis and Bob Dole.

The actor and director, who has been outspoken in support of Democratic causes in the past, said he has "complicated feelings" about President Barack Obama.

He said: "I voted for Obama last time although he got to be all things to all people then. And now he's got a record which makes it really different.”

The star believes Romney has been unable to connect with Americans during the campaign.

"I think Republicans really had a chance to win," Affleck said. "And they kind of ended up with like a sort of Mike Dukakis, Al Gore, Bob Dole type - who just couldn't get people to see him as a real person somehow.

"Romney just had such trouble coming off as just like the kind of person you see at the grocery store. And I truly believe that has cost him the election."

Affleck made the comments as he promoted his new film Argo which chronicles a joint effort by the CIA and the Canadian government to rescue six Americans from Tehran after the U.S. embassy was taken over by Islamist militants in 1978.

The actor, who has lobbied in Washington and visited Africa several times for various causes, said he was not optimistic whatever the outcome in November.

He said: "The world is a very tricky place in terms of foreign affairs. And really really we're in very bad shape economically.

"My worry is less about the presidential election than whether or not we're on a permanent downtrend. That really concerns me.

“Beyond the Obama administration and whoever the next - the Clinton administration - whoever gets elected next. That's my main concern."