MOSCOW — Russian officials on Friday denied that there was any deal in the works to free the Ukrainian helicopter pilot Nadiya V. Savchenko from a Moscow prison, casting doubt on reports that President Vladimir V. Putin of Russia and President Petro O. Poroshenko of Ukraine had agreed on her release during peace talks this week.

Mr. Putin’s spokesman, Dmitri S. Peskov, said Friday that Ms. Savchenko was not covered by a clause in the agreements negotiated in Minsk, Belarus, requiring the release of all war prisoners, and that she might stand trial in Russia.

“Savchenko is not a hostage,” Mr. Peskov said. “She is not illegally detained.”

In Washington, the State Department insisted that Ms. Savchenko’s release was provided for in the Minsk agreement. In the American view, the Kremlin’s refusal to free her would be a breach of the accord.

“We’ve called for Nadiya Savchenko’s release since she was first illegally spirited across the border and put on trial in Moscow,” said Jen Psaki, the State Department spokeswoman. “She’s a hostage of the Russian government, and she must be released immediately.”