Red Bull have control of the destinies of their Formula 1 drivers, according to Dr Helmut Marko, the boss of the energy drink company's driver programme.

At Red Bull Racing, rumours have linked Daniel Ricciardo and Max Verstappen with other teams for 2018, while Toro Rosso's Carlos Sainz is obviously keen to step up the grid after three years in F1.

However, Marko told Germany's Sport Bild that Red Bull are in charge.

"Ricciardo and Verstappen have fixed contracts," he said. "Ricciardo for 2018, and Verstappen with some clauses for even much longer."

The Austrian said that Red Bull are not willing to let any of them go.

"That also applies to Carlos Sainz," said Marko. "He is also bound to us in the longer team. Until 2019.

"Only we can end contracts - the drivers cannot."

Red Bull and Toro Rosso are currently third and fifth respectively in the team rankings.