BERLIN >> President Vladimir Putin of Russia on Thursday did not rule out a U.S. and Ukrainian proposal for a monthlong ceasefire, but he set down numerous conditions that would most likely delay any truce — or could make one impossible to achieve.

Putin’s comments highlighted the balance he was trying to strike, exuding confidence in Russia’s position on the battlefield while seeking to continue talks with the United States and avoid upsetting President Donald Trump, who has emerged as a key geopolitical partner for Putin.

President Volodymyr Zelenskyy of Ukraine later said the Russian leader set so many conditions “that nothing will work out at all or that it will not work out for as long as possible.”

Putin’s remarks came as Russia kept up its momentum in the key battle in the Kursk region of Russia, where Moscow’s forces appeared close to pushing Ukraine out of the territory it seized last summer.

“The idea itself is the right one, and we definitely support it,” Putin said, referring to the ceasefire proposal. “But there are questions that we need to discuss.”

Putin suggested that his conditions would include limits to Ukraine’s ability to mobilize more troops and import weaponry during a ceasefire — restrictions that would put Ukraine at a deeper disadvantage if the fighting restarted.