Speaking to Brussels-based journalists, Mr Chizhov warned against the negotiation process becoming "hostage to certain interests of individual member states of the EU, pursuing their own agenda that have little or nothing to do with the EU-Russia relations".

The 27-nation bloc is in the final phase of drafting the negotiating mandate - something that outlines precisely what the European Commission's manoeuvring space will be during the EU-Russia talks.

Diplomats hope the text will be approved without complaint by all EU foreign ministers at the end of this month (28-29 April), with the negotiations subsequently to be launched at a June EU-Russia summit in Siberia.

In order to open the talks, however, Vilnius needs to lift its veto - an issue linked to Russia's decision in July 2006 to disrupt oil supplies to Lithuania via the Druzhba pipeline.

According to one Lithuanian diplomat, the move has "proved Russia's failure to comply with transparency and credibility principles, undertaken under the Energy Charter provisions".

For this reason, Lithuania "needs practical steps ensuing from the negotiation process to institute real mechanisms of information exchange, early warning and confidence building."

"We expect to adopt a separate declaration on this issue," the diplomat told EUobserver.

But Mr Chizhov, also Russia's chief negotiator in the planned talks, said he wanted to see his EU counterparts to have as much freedom to manoeuvre as possible. "If their hands are tied behind their backs by national annexes, it will not be helpful for the outcome of the talks," he said.

"I am not questioning the principle of European solidarity. It is an understandable basis for the common EU foreign policy," the ambassador added, stressing: "I would prefer not to see this principle being tested on my country."

There is an additional sticking point, however, which centres around the Baltic country's request that the mandate clearly state that any EU member state can suspend the negotiations with Russia at any time.

"The union has to find the right place in its relations with Russia: a balance between isolation and yielding to any demand," the Lithuanian diplomat said, arguing that Russia does not hesitate to distance itself from its own previous commitments.

Several EU states, however, would like to avoid such wording in order to set a new tone in the EU's relations with Moscow following the election of Dmitrij Medvedev as new Russian president.

Efforts to launch negotiations on a new treaty of strategic partnership between the EU and Russia, covering areas such as the economy, external security or justice and home affairs, date back to 2006.

Relations are currently covered by the so-called Partnership and Cooperation Agreement, which came into force in December 1997 for an initial duration of ten years.

Although the treaty is automatically extended on an annual basis, both sides agreed to strike a new accord. Russia is the EU's largest neighbour, and a major supplier of energy as well as a significant market for EU goods and services.

Previously, the launch of negotiations was also blocked by Poland as a result of a trade dispute. But Warsaw dropped its opposition after Moscow agreed to end its embargo on Polish exports of meat and other meat products.