US Defence Secretary Pete Hegseth has ordered the withdrawal of about 5,000 troops from Germany within the next year, the Pentagon said.

Friday's announcement came after President Donald Trump threatened this week to remove troops from Nato ally Germany amid a row with its chancellor, Friedrich Merz, over the war that the United States and Israel have waged against Iran.

"We expect the withdrawal to be completed over the next six to 12 months," Pentagon spokesman Sean Parnell said.

"This decision follows a thorough review of the department's force posture in Europe and is in recognition of theatre requirements and conditions on the ground."

Merz has become a target of Trump's ire after saying on Monday that Iran is "humiliating" Washington at the negotiating table.

Trump said on Tuesday that Merz "thinks it's OK for Iran to have a nuclear weapon. He doesn't know what he's talking about!"

On Wednesday, Trump said Washington was "studying and reviewing the possible reduction" of US troops in Germany and that he would decide in a "short period of time".

During both of his terms in office, Trump has made a number of threats to slash US troop numbers in Germany and other European allies, saying he wants Europe to take on greater responsibility for its defence rather than depending on Washington.

But he now appears determined to punish allies who have failed to back the war against Iran or contribute to a peacekeeping force in the crucial Strait of Hormuz waterway, which Tehran's forces have effectively closed.

On Thursday, Trump said he may pull US troops from Italy and Spain due to their opposition to the war, saying that "Italy has not been of any help to us and Spain has been horrible, absolutely horrible".

"Yeah, probably, I probably will. Why shouldn't I?" he said.

As of December 31, there were 12,662 active-duty US troops in Italy and 3,814 in Spain. In Germany there were 36,436.

Speaking during a visit to Morocco, German Foreign Minister Johann Wadephul said on Thursday that Germany was "prepared" for a reduction in US troops and was "discussing it closely and in a spirit of trust in all Nato bodies."

The EU said on Thursday that the deployment of US troops in Europe was in Washington's interest, and that the United States was "a vital partner in contributing to Europe's security and defense." (AFP)

Edited by Robert Kemp