Training for Ukrainian forces and a more formal suspension of co-operation with Moscow are expected to be discussed at the Brussels meeting.
Some Russian troops - reported to number about 500 - are being withdrawn from the Ukrainian border, where the deployment of tens of thousands has raised fears of an incursion into other parts of the country.
The move was signalled by Vladimir Putin in a telephone call with German chancellor Angela Merkel, her office said, but 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 Mr Putin could mount similar incursions against the Baltic states of Latvia, Lithuania and Estonia, David Cameron last week confirmed that the Government was sending 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 cooperation 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,” Mr Cameron said.
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,” he told the BBC at the weekend.
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.
US President 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 cooperation with its Gulf partners and the preparations for the Nato summit in September - which is being held in Wales.