© Efrem Lukatsky/APUkrainian soldiers during exercises at a training ground outside Kiev.
Training for Ukrainian forces and a more formal suspension of co-operation with Moscow are expected to be discussed at the Brussels meeting on Tuesday.
Hours before the meeting was due to start Ukraine's parliament approved by a 235-0 vote a series of joint military exercises with NATO countries that would put US troops in direct proximity to Russian forces in the annexed Crimea peninsula.
The exercises will see Ukraine conduct two sets of military exercises with the US this summer - Rapid Trident and Sea Breeze - that have prompted disquiet in Russia in previous years.
Ukraine is planning two additional manoeuvres with Poland as well as joint ground operations with Moldova and Romania.
The Sea Breeze exercises have particularly irritated Moscow because they had on occasion been staged in Crimea - the home of Russia's Black Sea Fleet. In recent years the exercises have been moved to the Black Sea port of Odessa, where Ukraine also has a naval base.
"This is a good opportunity to develop our armed forces," acting defence minister Mykhailo Koval told MPs.
Some Russian troops - reported to number around 500 - are being withdrawn from the Ukrainian border. The move was signalled by Vladimir Putin in a telephone call with the German chancellor, Angela Merkel, her office said, but the US defence secretary, Chuck Hagel, called the scale of the build-up of forces "tremendous".
NATO's supreme commander in Europe, US General Philip Breedlove, has warned that the force on the border is "very, very sizeable and very, very ready" and raised the prospect that the Kremlin could even seek to take control of a Russian-speaking section of nearby Moldova.
Amid concerns that Putin could mount similar incursions against the Baltic states of Latvia, Lithuania and Estonia, David Cameron has ordered four RAF warplanes to the region to assist in "air policing".
NATO has increased surveillance in the region and mounted extra flights in Poland and Romania as well as suspending military co-operation with Russia - such as a proposed joint mission protecting a ship taking chemical weapons out of Syria.
"We should do everything we can to reassure our friends and colleagues in Latvia, Lithuania and Estonia and in Poland that we really believe in their Nato membership and the guarantees that we have given them," the British prime minister said.
Britain's defence secretary, Philip Hammond, has said the UK is considering increasing its participation in NATO military exercises in eastern Europe.
"Certainly one of the things we are looking at is a greater participation in exercises in the Baltic states, the eastern European NATO member countries as a way of reassuring them about our commitment to article five of the Washington treaty, the mutual guarantee," Hammond told the BBC.
Article five of the NATO treaty means that an attack on one nation in the alliance is viewed as an act of aggression against them all.
Barack Obama has said NATO countries must "meet the challenge to our ideals, to our very international order with strength and conviction".
A NATO spokesman said the meeting would "focus on increasing support for Ukraine and on the consequences of Russia's illegal military actions against Ukraine for NATO-Russia relations".
Other items on the agenda are relations with Georgia, the situation in Afghanistan, the alliance's co-operation with its Gulf partners and preparations for NATO's September summit in Wales.
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