Days before leaders of the transatlantic alliance are due to hold a summit, Merkel said NATO has been a "bulwark for peace and freedom" over the past 70 years.

"The preservation of NATO is in our own interest, more than during the Cold War," Merkel told parliament.

The German chancellor's strong defence of the bloc came after Macron said the alliance was suffering from "brain death".

Underlining Washington's changing role in playing world cop, Merkel noted that "the United States no longer automatically takes up responsibility when it's burning around us".

Nevertheless, "Europe cannot defend itself", she said, noting that it was therefore crucial to maintain the defence alliance.

To this end, Merkel pledged to keep raising Germany's defence spending, with an aim of reaching the goal of committing 2.0 percent of economic output by the early 2030s.

Robert O'Brien, national security counsellor to US President Donald Trump, welcomed the 2-percent pledge, in an interview with Bild daily.

But he said "it would be great if Germany took up its role as one of the leaders of the world."

As a leading economic power, "Germany has a duty to invest appropriately in defence for the benefit of its own defence and the defence of its alliance partners."