President Emmanuel Macron on Friday called Britain an ally whoever is in charge after the favourite to take over from Boris Johnson refused to say if the French leader was a "friend or foe".

Foreign Secretary Liz Truss was asked the question at a campaign event in the Conservative party leadership race late Thursday.

"If I become prime minister, I would judge him on deeds not words. The jury's out," she said to applause from Tory grassroots members.

On a visit to Algeria, Macron played down the comments.

"The British people, the United Kingdom, is a friendly, strong and allied nation, regardless of its leaders, and sometimes in spite of its leaders or the little mistakes they may make in grandstanding," he told reporters.

Britain and France are notably allies at the heart of the North Atlantic Treaty Organization political and military alliance and UN Security Council members.

But they have clashed on a number of issues in recent years, particularly after Britain's divisive departure from the European Union.

The two countries also have contrasting approaches to Russia's invasion of Ukraine.

During a press conference after visiting a cemetery in Algiers, Macron responded: "If we are not capable, between France and Britain, of saying whether we are a friend or enemy -- the term is not neutral -- we are heading towards serious problems."

He said "it's never good to lose your bearings in life" and added that if he were asked the question, he wouldn't hesitate "for a second".

"The United Kingdom is a friend of France," Macron said.

Outgoing British Prime Minister Boris Johnson, whose father recently gained French citizenship, switched to French to express warm support for Macron.

"I think I've always had very good relations with Emmanuel Macron. Emmanuel Macron est un très bon buddy de notre pays (very good buddy of our country)," Johnson told broadcasters while visiting an orthopaedic clinic in southern England.

Johnson added: "I think the relations between the UK and France are of huge importance. They have been very good for a long time, ever since the Napoleonic era basically, and I think we should celebrate that."

The Napoleonic wars ended in 1815 with defeat at Waterloo against allied troops commanded by the Duke of Wellington.