Ukraine’s drone attacks on airfields deep inside Russia on Sunday was a strategic and symbolic blow that military analysts said was designed to slow Moscow’s relentless bombing campaign and to demonstrate that Kyiv can still raise the cost of war for the Kremlin.

Although the full extent of the damage is unknown, the attacks, known as Operation Spider’s Web, showed how Ukraine is adapting and evolving in the face of a larger military with deeper resources. Using drones, Kyiv has been able to push Russia out of much of the Black Sea, limit its gains on the front lines despite Ukraine’s own troop shortages, and hamper Russia’s ability to amass large concentrations of forces to for major offensives.

The operation on Sunday, along with extensive bombardments on Ukrainian cities by Moscow, also complicate ongoing efforts for diplomacy. Delegations from both sides met Monday for peace talks in Istanbul, with no breakthrough on a cease-fire announced.

After the attacks, there were calls for a swift response across Russian media, and Ukrainians braced for retaliation even as they celebrated an operation that gave their beleaguered nation a much needed morale boost.

Both sides have put out assessments that were not immediately verifiable.

Ukraine said that 117 drones were used in the attacks, known as Operation Spider’s Web, and that 41 Russian aircraft were destroyed or damaged.