"We will always protect ethnic Russians in Ukraine, as well as the part of Ukrainian people who ... feel part of the wider Russian world, and we will not only monitor this but also react," Putin said during a visit to Austria. "I hope that armed forces will not be necessary for this."
Putin asked Russian lawmakers on Tuesday to revoke a resolution allowing him to invade Ukraine in a shock change of heart that Kiev hailed as the "first practical step" in defusing the months-long crisis.
The Russian leader however insisted that a seven-day truce between separatist rebels and forces loyal to Kiev in Ukraine's restive east be followed by concrete talks.
"It is not enough to announce a ceasefire, there should be the beginning of negotiations," Putin said.
"If we keep hearing, here is seven days ... and then this time is not used for a single attempt at reaching an agreement with eastern Ukraine, then all the efforts will be in vain, there will be no result."
Months of fighting in eastern Ukraine have claimed the lives of around 390 civilians and fighters on both sides.