Hamilton: I don’t know where [Horner] rumours have come from

Ferrari have yet to win in 18 rounds of the 24 race season and despite team principal Fred Vasseur being handed a contract extension in July, the talk about the Frenchman's future has failed to die down.

The latest speculation, in Italy and England, suggested Ferrari had held exploratory talks with Horner -- one of the sport's most successful bosses of all time but sacked abruptly in July.

Horner and Ferrari have not commented, although Aston Martin boss Andy Cowell said at this month's Singapore Grand Prix that Horner had been in touch with team owners across the paddock.

"I don’t know where the rumours have come from, so I can’t really shed much light on that. It’s a little distracting for us as a team," Hamilton told reporters at the U.S. Grand Prix on Thursday. "The team have made it clear where they stand in terms of re-signing Fred.

"Fred, I, and the whole team are working really hard on the future. These things aren’t helpful," added the seven-times world champion.

"Everyone back in the factory is working incredibly hard, focused, and these sorts of rumours can sometimes be distracting," the Briton maintained.

Vasseur was instrumental in signing Hamilton, 40, from Mercedes but the sport's most successful driver has yet to stand on the podium in Ferrari red since he joined in January.

Asked again whether he knew if there was any truth to the reports and whether he thought it was a good idea for Horner to become principal, Hamilton replied: "I don't, and I’m not going to entertain rumours."

It was not clear which part of the question the 'I don't' referred to.

Hamilton said the focus was firmly on next year, when the sport starts a new engine era with sweeping rule changes that could shake up the pecking order.

"I’m really looking at the next six races as, ultimately, test weekends in terms of continuing to learn and improve on our processes," he said.

Hamilton counts Austin's Circuit of the Americas as a favourite track and has won there five times.

(Reporting by Alan Baldwin)