The European Commission has signed a preliminary agreement with the vaccine developers but it requires separate approval from EU member states.
Lithuania has earlier decided to buy 1.86 million doses from AstraZeneca and 1.24 million doses from Janssen Pharmaceutica NV.
Health Minister Aurelijus Veryga has said the government wants to secure enough doses to vaccinate 70 percent of the country's population.
Prime Minister Saulius Skvernelis has said that Lithuania might have to pay up to 125 million euros for COVID-19 vaccines, but it could sell surplus doses to the Eastern Partnership countries.
In addition to the preliminary agreements with AstraZeneca, Janssen Pharmaceutica NV and Sanofi-GSK, the European Commission has also concluded exploratory talks with CureVac, BioNTech-Pfizer and Moderna.
The EU's executive body said on Monday that it was very close to signing a preliminary agreement with Pfizer and BioNTech for 300 million doses of their new coronavirus vaccine.
The companies announced on Monday that their jointly-developed vaccine was 90 percent effective at preventing COVID-19.