US President Donald Trump has ordered the US military to remove nearly 9,500 troops from Germany in a move likely to raise concerns in Europe about the US commitment to the region.

The move would reduce US troop numbers in Germany to 25,000, compared with the 34,500 currently there, a senior US official said.

The Wall Street Journal says officials in the Trump administration have discussed cutting US troops in Germany since last September.

The newspaper says White House National Security Advisor Robert O'Brien has already ordered the troop reduction in a signed memorandum.

The US troops in Germany are said to play a key role in ensuring security in Europe. But Trump argues that the US burden is unfairly heavier than that of NATO allies in Europe. Especially, Trump has repeatedly complained that Germany pays too small a portion.

US media noted that Trump's dissatisfaction over the burden-sharing is behind the latest decision to slash US troops in Germany.

Concerns are expected to be voiced over the move in the United States and other countries as the troop reduction could affect European security.