Mr. Tillerson’s statement Sunday in Kiev was more definitive on the issue of sanctions than his boss’s tweet, perhaps a reflection of the political reality in Washington, where the Senate voted, 97 to 2, last month to toughen sanctions because of Russia’s continued intervention in eastern Ukraine, Moscow’s attempts to intimidate former Soviet states and the conclusion of American intelligence agencies that Russia had interfered in the 2016 election.

The administration has sought to water down the sanctions bill to give itself more leeway in dealing with Russia, an effort that was viewed by many Republicans and Democrats as a way to relax sanctions without congressional approval.

It was unclear how the Russians might react to Mr. Tillerson’s comments insisting that Moscow restore Ukraine’s territorial integrity. A few days ago, Mr. Tillerson announced he was appointing a new special envoy, Kurt Volker, to help settle the dispute in Ukraine in part at the request of Mr. Putin. And Russian officials believed they had made progress in Mr. Putin’s meeting with Mr. Trump.

As Mr. Tillerson spoke Sunday, Mr. Volker sat in the front row, and he was to remain in Kiev after Mr. Tillerson departed to discuss how to enforce the largely ignored Minsk accord agreed in 2015 that envisioned a way out of the Ukraine impasse.

During his short news conference in Kiev with Mr. Poroshenko, who took office after one of Mr. Putin’s acolytes was pushed from power, Mr. Tillerson also declined to say whether Mr. Trump, during his meeting with the Russian president, accepted Mr. Putin’s denials that Russia was involved in efforts to influence the 2016 election.

Mr. Tillerson was the only other senior American official in the room during the presidents’ meeting. His Russian counterpart, Sergey V. Lavrov, the Russian foreign minister, told reporters after the meeting in Hamburg that Mr. Trump had been persuaded by Mr. Putin’s arguments.