Litgrid spokeswoman Vilija Railaitė told BNS that the top executives of Polska Grupa Energetyczna Operator and Litgrid had signed the agreement on 1 December, 2011.
She could not say why there had been no public announcement about the signing of the deal. Some sources told BNS at the start of this year that the parties had agreed not to comment on the deal.
The signing of the agreement means the launch of implementation, or construction, stage, which is planned to be completed by the end of 2015.
The signing of the deal had been expected back in the autumn of 2010, and then in late 2011. According to media reports, some officials guessed that LitPol Link was a precondition for Poland's Polska Grupa Energetyczna Operator to invest in Lithuania's Visaginas nuclear power plant project.
It was also said that officials were waiting for Poland to decide if its new government would have two separate ministries for economy and energy, as well as for a good political opportunity.
Kęstutis Škiudas, advisor to Lithuania's prime minister, was quoted last November as saying that Lithuanian and Polish representatives had signed a draft agreement on investments in LitPol Link and that the document had been approved by the management boards of Poland's PSE-Operator and Lithuania's Litgrid.
Under the agreement, PSE-Operator and Litgrid are the operators of the new power line.
LitPol Link's shareholder agreement, signed back in 2008, provided for carrying out preparatory work for a 400-kilovolt overhead power transmission line. The 150-kilometer double circuit power line will link Elk, in northwestern Poland, to the southern Lithuanian district of Alytus.
The interconnection is planned to be operational by the end of 2015 with a capacity of 500 megawatts, to be raised to 1,000 MW by 2020.
LitPol Link is one of Lithuania's strategic energy projects. The interconnection will link the electricity transmission infrastructure of the three Baltic countries to that of Western Europe and pave the way for an integration of the electricity markets.
Poland has received 213 million euros in EU aid for upgrading transmission lines in the northeastern part of the country as part of the LitPol Link project.