The ex-Soviet state's Environment Ministry said the European Commission, the EU executive, had pledged in a letter to seek full report."Hopefully the European Commission will be able to break the Russian wall of silence," the ministry said in a statement.
It said Russian oil major LUKOIL intended late this year to start exploiting the D-6 Kratsovskoye oilfield near the border between Russia's Kaliningrad enclave and Lithuania.
LUKOIL planned to extract 12,000-14,000 barrels per day of high quality crude a year over 30 years.
The ministry said Russia had ignored its own requests for an expert assessment, as well as those of the Helsinki Commission and the UNESCO World Heritage Committee.
Lithuanian officials have said frequent storms at the field increased the danger of an oil spill that might threaten the Curonian spit, a 98 km (60 mile) long sandy peninsula between Lithuania and Kaliningrad, which is a UNESCO World Heritage site.
"Unsafe oil extraction 22 kilometres from the Curonian Spit and just seven to eight kilometres from Lithuania's sea border, which next year will be a European Union border, is good reason for the international community's concern," the ministry said.
Officials at LUKOIL, which has said the project poses no environmental risk, were not immediately available for comment.
Lithuania was one of 10 countries to complete EU accession negotiations in December and expects to join the bloc in 2004.