The company, which accepted a government rescue package last month, said that it had recorded a net loss in the first six months of the year of 12.3 billion euros ($12.5 billion).
"Uniper has for months been playing a crucial role in stabilising Germany's gas supply at the cost of billions in losses resulting from the sharp drop in gas deliveries from Russia," CEO Klaus-Dieter Maubach said in a statement.
The German government agreed in late July to take an around 30-percent stake in Uniper, which was threatened with bankruptcy as a result of the crisis.
Maubach said on Wednesday that the bailout would "prevent a chain reaction that would do much more damage".
"Our top priority now is to swiftly implement the stabilisation package," he added.
Chancellor Olaf Scholz interrupted his summer holiday to announce the rescue plan, calling Uniper a "company of vital importance for the economic development of our country and for the energy supply of our citizens".
Uniper said the "volatile environment" meant that it could not provide an earnings forecast for the current financial year.
But it expected "to record negative earnings owing to the significant reduction in Russian gas deliveries".
Russia's war in Ukraine has caused turmoil in European energy markets, especially in Germany, which is heavily dependent on Russian gas.
EU states have accused Russia of choking supplies in retaliation for Western sanctions over the war, with Germany charging that Moscow is using energy as a "weapon".
Russia in July restored critical gas supplies to Europe through Germany via the Nord Stream pipeline after 10 days of maintenance, but at low volumes, and suspicions linger that the Kremlin may trigger an energy crisis on the continent this winter.