Mr Miliband's most recent overseas visit was to Sri Lanka
The government is seeking to rent a private jet for the use of Foreign Secretary David Miliband.
A tender for the hire of a charter aircraft was issued in February and will last two years, it is understood.
The ministerial code states that scheduled flights should be used unless deemed impractical.
The Foreign Office said its decision was aimed at securing value for money following changes in the availability of RAF flights for ministers.
A spokesman said: "Unlike a lot of other countries we don't have a Foreign Office plane.
"We always try to use commercial airlines but sometimes that is not practical. Until now we have been able to use the RAF in those circumstances.
"Changes in the RAF mean we need the ability to charter aircraft sometimes at short notice - value for money is a top priority."
The contract for the aircraft hire is yet to be issued. According to the News of the World, the tender document states that officials are looking for "a good quality aircraft for overseas visits by the Foreign Secretary".
The company, the document adds, must "provide a first class service" and be able to "provide an aircraft sometimes within a few hours' notice".
In 2008, Mr Miliband, who recently flew to Sri Lanka for an official visit, made more than 20 state trips to countries including the US, Turkey and Syria.
In March last year, the government scrapped plans to buy two private jets to fly the prime minister and the Royal Family around the world, citing cost and environmental reasons.