The agreement was announced in a statement issued by the foreign ministers of Lithuania, Poland, Sweden, and Slovenia, who were meeting in Vilnius.
Lithuania says it has won a diplomatic victory and that the country's most urgent concerns will be included in future EU-Russia talks.
"We have reached a big victory," Violeta Gaizauskaite, a spokeswoman for the Lithuanian Foreign Ministry, tells RFE/RL. "The European Commission has agreed to include into the talks with Russia all the questions we are concerned about. Now, probably the formulations will have to be polished because, as you know, other EU countries have to give their approval to what has been agreed to. But the main point is that the EU starts to understand our demands and our objectives, and the EU has taken into account our most important interests."
A statement issued by the four foreign ministers said: "We have found ways to reflect in the mandate of the talks the issues of the Druzhba pipeline, issues of legal cooperation with Russia, and frozen conflicts."
Lithuania had threatened to veto EU talks on a new partnership accord with Russia in protest at Moscow's decision to close the Druzhba pipeline, which feeds Russian oil to Lithuania's only oil refinery.
"We have reached an agreement on the formulation and the annex to the mandate, which takes account of Lithuania's and Poland's joint energy concerns," Sikorski said.
Russian Legal Cooperation
Lithuania also wants a declaration on Russian legal cooperation to be included in its negotiating mandate. Vilnius wants Russia to help investigate who was behind the decision to send Soviet tanks into Lithuania in January 1991, which resulted in the deaths of 14 people. Hundreds were injured. Vilnius also wants Russian cooperation into an investigation into the killings of seven unarmed police and customs officers in independent Lithuania in the summer of that same year.
Lithuanian also wants Moscow to work toward resolving the "frozen conflicts" in Moldova and in Georgia, which Vilnius says are connected to the security of Lithuania and, in turn, the EU.
Georgia is involved in a bitter dispute with Russia over the breakaway regions of South Ossetia and Abkhazia, run by pro-Moscow separatists in the presence of Russian troops. Russian-speaking residents of Moldova's Transdniester region have declared unilateral independence in an area where Russian forces also are present.
Vaitiekunas stresses that progress in resolving these conflicts is a "direct condition" for success in the talks between Russia and the EU.
Concrete Guarantees
Lithuanian Foreign Minister Petras Vaitiekunas says Vilnius has received concrete guarantees.
"Today, I must acknowledge that Europe is united. Europe is united in terms of security, justice, and global law," Vaitiekunas says. "In principle, most of Lithuania's requirements have been taken into account. All Lithuanian interests have been taken in account in written form."
Vaitiekunas spoke after a meeting May 11 with three other EU foreign ministers -- Sweden's Carl Bildt, Poland's Radoslaw Sikorski, and Slovenia's Dimitrij Rupel, whose country holds the rotating EU presidency until June.
The agreement will nonw be discussed at a May 26 meeting of the EU's Council of Foreign Ministers.