MOSCOW — The United States will deepen its involvement in negotiating a solution to the Ukraine crisis, with a senior State Department official, Victoria J. Nuland, to hold a day of talks on Monday with Russian officials on buttressing a rickety peace agreement.

Until now, the peace agreement reached in February by the leaders of Russia, Ukraine, Germany and France has curbed the worst violence between the government forces and the Russian-supported separatists in southeastern Ukraine. Fighting continues at various flash points, however, and work on carrying out political and economic measures in the agreement, negotiated in Minsk, Belarus, has sputtered.

“There is less firing, but none of us should be satisfied with the results,” Ms. Nuland said Saturday at a news conference in Kiev, Ukraine. “So that’s why we want to push harder on all of these things and see what we can achieve in the coming days and weeks.”

She arrived in Moscow for negotiations just days after Secretary of State John Kerry met for four hours with President Vladimir V. Putin in the southern resort of Sochi to discuss Ukraine, the Iranian nuclear negotiations and the Syrian conflict, among other issues. It was the first visit by a senior American official since the Ukraine crisis erupted in February 2014.