Western leaders are planning a powerful show of unity at a NATO summit this week against what they see as Russian aggression in Ukraine, but the measures will remain limited due to a lack of political consensus on direct intervention.

The planned deployment of thousands of NATO troops and military equipment in Eastern Europe is intended to reassure NATO member states in the former Soviet bloc and is bound to anger Russia as it will challenge a key NATO-Russia deal.

But the summit in Wales on Thursday and Friday is likely to stop short of an outright challenge to Moscow on the spiralling conflict in eastern Ukraine, which is threatening to degenerate into all-out war between Russia and Ukraine.

"The likelihood of any type of overt military intervention is highly unlikely," said Robin Niblett, director of the Royal Institute for International Affairs (RIIA) in London.

"There is no support for it at an alliance level. No one is going to go on their own," he said, pointing out that there is no obligation on NATO to act as Ukraine is not a member and does not enjoy the same principle of "collective defence".

Some NATO members like Romania have urged the alliance to supply Ukraine's military and there has been a plea from a group of hawkish US senators for President Barack Obama to do the same but other allies are being far more cautious.

Xenia Wickett, an expert at the RIIA, also said that the summit should be seen as "a waymarker, not an end point" and much would depend on implementation of summit decisions.

Here are the main measures currently planned by NATO:

TROOP DEPLOYMENTS: NATO Secretary General Anders Fogh Rasmussen has said the summit will aim to approve a "readiness action plan" which will include rotating troops and equipment through facilities in Eastern Europe.

"The bottom line is you will in the future see a more visible Nato presence in the east," Rasmussen said in an interview with five newspapers ahead of the summit.

The precise status of the facilities would be left deliberately vague as establishing "permanent" bases for NATO in Eastern Europe would contravene the NATO-Russia Founding Act of 1997 -- an agreement that some commentators have said is already worthless because of Russia's actions.

Rasmussen said the plan could also involve strengthening infrastructure like ports and airports, increasing military exercises and boosting intelligence-sharing.

MILITARY FUNDS: NATO would establish four "trust funds" to help finance Ukraine's military logistics, command and control structures and cyber defences, as well as to pay soldiers' pensions, including for wounded personnel.

Rasmussen has said the funds would help Ukraine "build the capacity of their security sector" and pointed out that some members had already pledged "concrete financial contributions" -- although no figures have been mentioned.

The funds are in any case for the "medium-to-long term".

Ukrainian President Petro Poroshenko, who is scheduled to attend the summit, has said he expects individual NATO member states to increase their weapons contributions.

"Ukraine is making a whole series of demands. It would be the allies rather than NATO who would respond on a bilateral basis," a senior official said on condition of anonymity.

UKRAINE IN NATO?: Ukraine's government is planning to submit a bill in parliament to resume its application for NATO membership, a procedure that was interrupted in 2010 under the pro-Moscow Viktor Yanukovych who was president at the time.

Ukraine's future membership was welcomed by NATO leaders at a summit in Bucharest in 2008, riling Russia, although in reality it is a distant prospect since Ukraine's Soviet-era arsenal would first have to be upgraded to NATO standards.

Moscow has requested that Ukraine declare neutrality and in reality few members can stomach the prospect of Ukraine joining, which could oblige NATO to intervene in the conflict.

NATO-RUSSIA TIES: NATO already suspended most of its practical cooperation following the annexation of Crimea earlier this year and fears about Russian expansionism, although it is still formally sticking to the NATO-Russia Founding Act.

The alliance has also stepped up fighter jet and reconnaissance missions over the Baltic states, deployed warships in the Black and Baltic Seas and ramped up military exercises in the region.