"Based on the initial information, our employees died of asphyxiation from gas accumulated in a pipeline. One of the employees lost consciousness in a well during the installation of a pipeline, and the other two rushed to help him but also died," Marius Svaikauskas, CEO at Vilniaus Vandenys, said in a statement.
The incident happened during planned repairs, the company said.
"We are shocked as it's a true tragedy for our whole company. We offer our deepest condolences to the families of our employees. Our effort is now focused on supporting the families. The company will provide all necessary assistance to the relatives. We are also making every effort to identify the circumstances of this incident," Svaikauskas said.
An investigation is underway and Vilniaus Vandenys and all services looking into whether all safety requirements were met during the repairs.
Vilnius County Police says the men were aged 51, 53 and 65.