Incoming EU chief congratulates Britain's Johnson

The new head of the European Commission, Ursula von der Leyen, congratulated incoming British prime minister Boris Johnson on Tuesday, but warned they faced "difficult" and "challenging" times ahead.

"Congratulations to Boris Johnson for being nominated as prime minister," she said at a meeting with French President Emmanuel Macron in Paris. "I am looking forward to having a good working relationship with him.

"There are many different and difficult issues to tackle together. We have challenging times ahead of us.

"I think it is very important to build up a strong and good working relationship because we have the duty to deliver something that is good for people in Europe and in the United Kingdom," she added in English.

Von der Leyen, a former German defence minister, is set to take office one day before the current deadline for Brexit of October 31, with Jean-Claude Juncker nominally in control of the EU executive until then.

Macron, who has criticised Johnson in the past, also congratulated the incoming British PM who is expected to be asked to form a government by the Queen on Wednesday.

"I congratulate Boris Johnson and I will call him when he is officially prime minister," Macron said.

"I want very much to work with him as quickly as possible and not just on European subjects and the continuation of negotiations linked to Brexit, but also on international issues on which we coordinate closely with Britain and Germany... like the situation in Iran," he added.

In an interview in March 2017 after Britain's European referendum the year before, Macron said Johnson "enjoys giving flamboyant speeches but has no strategic vision" and he held him responsible for the "crime" of Brexit.

The French leader also paid tribute to outgoing British leader Theresa May on Tuesday in a message that was perhaps also destined for Johnson's ears.

He said May had she carried out her duties with "a lot of courage a dignity". "She never blocked the functioning of the European Union," he added.