After giving the strongest indication yet that Ukraine’s counteroffensive is imminent, President Volodymyr Zelensky on Saturday urged his compatriots to personally thank the volunteers and soldiers fighting Russian troops, in a sign of how grim the next phase of the war could be.

Mr. Zelensky singled out more than a dozen soldiers by name, noting that in his nightly speeches he usually thanks specific units or brigades. But Saturday’s address was, he said, a collection of “more personal words of gratitude to particular warriors.”

His plea to thank soldiers, even if only on social media, followed similar statements from his top military commanders, who have said they are ready for the counteroffensive despite a lack of air defense systems. And his defense minister rebuffed peace talks at a summit of military officials in Singapore on Saturday. Ukraine has also grown bolder, attacking behind Russian lines in past months, another sign of the shifting tone of the war.

Earlier on Saturday, The Wall Street Journal published an interview with Mr. Zelensky in which he said that Ukraine was ready for the counteroffensive but warned that “a large number of soldiers will die” because Russia retains the upper hand in air power. In addition to the billions of dollars of military aid and advanced weapons that Ukraine has already received from the United States and Europe, Mr. Zelensky has been pushing his allies for more air defense systems and F-16 fighter jets.

And Ukraine continues to reject proposals of peace talks that do not involve Russia first withdrawing its forces from occupied areas. The latest such proposal was made by Prabowo Subianto, the Indonesian defense minister, on Saturday at the international gathering in Singapore.

Mr. Zelensky’s comments were published a week after Ukraine’s top military commander signaled that the counteroffensive was about to be launched, which analysts have said may have already begun in one form or the other. It is likely to be centered in southern Ukraine and focus on land routes between Russia and Crimea, the Ukrainian territory Moscow illegally annexed in 2014.

“There is no perfect time to launch the Ukrainian offensives, but there will be a time that is optimum for Ukrainian force preparations and where they are most able to exploit Russian weaknesses,” Mick Ryan, a military analyst and retired Australian general, wrote Sunday on Twitter. “That time is close.”