Spain has suspended all troop transport flights chartered with a Nato agency following a fatal plane crash in Turkey last week.
Thick fog is said to have caused the crash
Defence Minister Federico Trillo said the ban on contracts with the Nato Maintenance and Supply Agency (Namsa) would last until investigations into the crash were completed.
The decision follows reports of criticism by the military of the fleet of Ukrainian and Russian planes used to transport troops to conflict zones.
Sixty-two Spanish servicemen returning from a peacekeeping mission in Afghanistan and 13 crew died in last Monday's crash near the north-western Turkish town of Trabzon.
The Spanish newspaper El Mundo has reported that Spain is planning to sue Nato to help pay compensation to the families of the victims.
Spain's Defence Ministry has as yet made no comment on the report.
The Ukrainian Yak-42 plane hit a mountain near the Black Sea town after the pilot apparently tried to land in fog in order to refuel.
The aircraft was flying from the Kyrgyz city of Bishkek to Zaragoza in Spain.
Spanish soldiers are said to have criticised the state of some of the chartered aircraft.
The El Pais newspaper said troops returning to Madrid from the Iraqi city of Basra last Thursday complained about a Russian Ilyushin-76 transport plane they were flying in.
Last week's crash was the third by a Ukrainian-operated jet in the last six months.
On 9 May, around 160 people died when the cargo-bay door on an Ilyushin-76 transport aircraft run by Ukraine's Defence Ministry and piloted by a Ukrainian crew flew open over the Democratic Republic of Congo.
In December, 44 people, mainly Ukrainians, died when a Ukrainian-made Antonov An-140 crashed in Iran.
Correspondents say Ukrainian charter companies have become major players in international military and commercial missions over the last 10 years.
They offer lower rates and cheaper crews in the fiercely competitive market.