The US has threatened to withdraw thousands of troops stationed in Germany amid a dispute with Angela Merkel’s government over defence spending.

Richard Grenell, the US ambassador in Berlin, warned that his country could pull out some of its forces if Germany continues to fall short of the alliance’s spending target of 2 per cent of GDP.

“It is actually offensive to assume that the US taxpayer must continue to pay to have 50,000-plus Americans in Germany, but the Germans get to spend their surplus on domestic programs,” Mr Grenell told Germany’s DPA news agency.

The remarks will add to concerns that the Nato alliance is becoming strained by President Trump’s impatience with German military spending.

The US currently has just over 35,000 troops stationed in Germany, together with 17,000 American civilian support staff.

By far the biggest US deployment in Europe, it is a legacy of the Cold War, when West Germany lay on the frontline with the Soviets and was considered Nato’s first line of defence.

But in what is a clearly coordinated message from the Trump administration, Mr Grenell is not the only US diplomat to suggest the longstanding alliance with Germany is in trouble.

Georgette Mosbacher, the American ambassador in Warsaw, made clear that US has other options when she called for the troops in Germany to be transferred to Poland.