NATO launches its biggest military exercise since 2002 on Saturday, putting 36,000 alliance soldiers through their paces in Italy, Spain and Portugal to boost preparedness against the backdrop of the Ukraine crisis.

NATO launches its biggest military exercise since 2002 on Saturday, putting 36,000 alliance soldiers through their paces in Italy, Spain and Portugal to boost preparedness against the backdrop of the Ukraine crisis.

"Trident Juncture" runs from Saturday through to November 6 and involves personnel from more than 30 countries, the NATO Allied Joint Force Command center based in the Dutch city of Brunssum says on its website.

The exercise will also involve Canada, Norway, Germany, Belgium and the Netherlands, together with operations in the Atlantic and Mediterranean.

"Trident Juncture 2015 will demonstrate NATO’s new increased level of ambition in joint modern warfare and will showcase a capable, forward-leading alliance equipped with the appropriate capability and capacity to meet present and future security challenges," the command center said.

The long-planned exercise has taken on a new significance after Russia's annexation of Crimea last year and its support of pro-Moscow rebels in eastern Ukraine.

In response, NATO has rotated forces through newer east European members such as the Baltic states and Poland who fear Russia wants to restore its influence over the Cold War-era satellites.

The 28-nation alliance, led by the United States, has also increased its preparedness levels in the face of a whole series of evolving threats exemplified by events in the Ukraine and conflict and upheaval across the Middle East and North Africa.

In September last year, NATO leaders agreed to set up a new, very rapid response force able to put boots on the ground within days.

The Brunssum command centre said the Trident Juncture exercise would allow NATO to certify the staff as ready to lead this rapid response force if it is formally activated as expected next year.