Russia and its ex-Soviet allies Kazakhstan and Belarus told World Trade Organisation members on Wednesday they were suspending individual accession efforts to look at ways of joining the body together as a customs union.

But diplomats and officials said the proposal -- announced to widespread surprise last week by Russian Prime Minister Vladimir Putin -- was fraught with legal and technical difficulties and it remained unclear how it would work.

"All three countries have suspended the bilateral and multilateral WTO accession negotiations until we find a common decision with WTO members on how we can accede to the World Trade Organisation ... as a customs union or single customs territory," said Kazakhstan's chief WTO negotiator, Zhanar Aitzhanova.

The three countries are suspending, not cancelling, their applications, Aitzhanova, who is Kazakhstan's vice-minister for industry and trade, and Russia's chief negotiator Maxim Medvedkov told reporters after they and Belarus had briefed the WTO's 153 members on the plan.

"I would like to underline that it's not aimed at delaying the process because our joint aim continues to be accession as quickly as possible," Medvedkov said.

But diplomats said further delay to the accession process that has already taken 16 years in the case of Russia, the biggest country still outside the WTO, seemed inevitable.

Once WTO members have agreed a legal basis for a joint candidacy -- and there is no precedent for a customs union joining the group that referees world trade as a single entity -- it will be necessary to harmonise the agreements already made separately with the different countries.

"It cannot be excluded, if this track will be pursued, that it could delay the accession process of Russia because there are lots of legal issues that need to be resolved," said Stefan Johannesson, the Icelandic diplomat who chairs Russia's membership negotiations.

Medvedkov said he hoped to produce proposals in weeks rather than months on how the three countries could pursue a joint membership application.

He said they are examining all options for joining as a customs union while preserving what has been agreed so far in individual negotiations.

The three are keen to develop regional economic integration, and the plan fits in with Putin's interest in promoting Russia as the dominant power among former Soviet republics.

Russia also decided to pursue the customs union approach out of frustration at the lack of progress in its individual negotiations, a western diplomat quoted Russian officials as saying.

WTO rules do not provide for countries to join as a customs union, although they lay down the terms under which existing members can form a customs union, allowing them to override the WTO's basic principle of non-discrimination.