Donald Trump is demanding that allies with US troops stationed in their countries pay for the privilege in a concerted drive to bring down costs.

The US president wants such countries to not just cover the full cost of US troop deployment but also pay America an extra amount for the service.

Mr Trump upset negotiations with South Korea late last year by demanding “cost plus 50”, which means paying the full cost of deployment plus a further 50 per cent.

The demand contributed to just a one-year deal being signed with South Korea, where 28,000 US troops are stationed, rather than the usual five-year agreement.

The push has alarmed experts and former officials who warned that seeing the arrangements in pure cost terms downplays the strategic advantage it brings America.

Details of the drive were first reported by Bloomberg News and confirmed by The Daily Telegraph.