KYIV, Ukraine >> As momentum builds for a ceasefire with Russia, Ukraine has all but lost a valuable bargaining chip.

The Ukrainian army stunned Russia in August by attacking across the border and taking control of an estimated 500 square miles of land. It was a much-needed morale boost for Ukraine — but more importantly, the country’s leaders believed the capture of Russian territory might help in any future peace negotiations with its enemy.

Now, after months of intense pressure from Russian forces supported by troops from North Korea, Ukraine only holds about 30% of the Russian land it had seized and its forces are in retreat after a rapid near-defeat in the city of Sudzha.

The Ukrainian army on Thursday was trying to build up defensive lines near the border to prevent Russia from turning its assault on Sudzha into a launchpad for advancing into northeastern Ukraine.

Politically speaking, the retreat from large parts of Russia’s Kursk region could be a moment of reckoning for Ukrainian President Volodymyr Zelenskyy and his military advisers. The invasion of Kursk was intended to redirect Russian forces from inside Ukraine — and the land gained was supposed to help Ukraine get back at least some of the 20% of its country taken by Russia since its full-scale invasion in February 2022

But many soldiers and commanders have long questioned whether it was worth diluting their forces available to defend Ukraine, and those doubts only grew as the retreat from Kursk accelerated.

Russian President Vladimir Putin said Thursday that he agrees in principle with a U.S. proposal for a 30-day ceasefire in Ukraine, but that the details still need to be worked out. Putin made the remarks just hours after the arrival of President Donald Trump’s envoy in Moscow.

Combat is ongoing in the periphery of Sudzha as some Ukrainian soldiers try to fight their way out of Russia’s Kursk region back into the neighboring Sumy region of Ukraine.

Ukrainian soldiers and commanders fear that Russia’s air superiority will enable them to wipe out the logistics routes vital to sustaining the soldiers who are still in Kursk.

Russia has retaken control of about 70% of the territory Ukraine captured in the first weeks of its August incursion into Kursk, according to the Institute for the Study of War in Washington.

To flee the Kursk region, Ukrainian soldiers must walk dozens of kilometers to get back into Ukraine, while avoiding Russian forces. Some soldiers are angry that commanders did not order them to withdraw weeks ago, when it would have been safer to do so.