NATO exercises in April and June will test progress of a new rapid reaction force created in the wake of the Ukraine crisis, alliance officials said Wednesday.

"This will be the first opportunity to see the interim Very High Readiness Joint Task Force in action," a NATO official told a briefing at the alliance's military HQ in the Belgian city of Mons.

Stung into action as the Ukraine crisis deepened, NATO leaders agreed in September to create a new "spearhead" force of about 5,000 troops able to deploy anywhere within a couple of days.

This VJTF unit is due to be operational by 2016, with command centres being set up in NATO's east European members -- many once ruled from Moscow -- so that the troops hit the ground running.

They would be followed by the rest of the NATO Response Force, expected to number up to 30,000 soldiers in all, to make sure that the alliance, born in the Cold War to deter the Soviet Union, can meet modern-day threats.

"The first exercise will focus on rapid preparation and deployment," said the NATO official who asked not to be named.

"In the second exercise, they will be tested on their ability to deploy from Germany, the Netherlands, Norway and the Czech Republic to the Zagan training area in western Poland ... to respond to an unfolding crisis," the official said.

"It will be a very dynamic exercise, the first time that the VTJF will actually train live," the official added.

NATO officials stressed that the exercises did not target any specific country and were part of alliance efforts to meet a broad spectrum of threats, in the east but also in the Middle East and North Africa.

Announcing the Readiness Action Plan at the September summit, then NATO head Anders Fogh Rasmussen said: "This decision sends a clear message -- NATO protects all allies at all times."

"This is a demonstration of our solidarity and our resolve," Rasmussen said.