MOSCOW — President Vladimir V. Putin of Russia accused the Ukrainian government on Wednesday of plotting terrorist attacks in Crimea, and threatened to respond. His Ukrainian counterpart called the accusations “fantasies.”

Mr. Putin, speaking at the Kremlin, said two Russian servicemen had been killed while confronting people he described as the plotters.

“There is no doubt that we will not let these things pass,” Mr. Putin said in remarks broadcast on state television.

“But I would like to turn to our American and European partners,” he said. “I think it is clear now that today’s Kiev government is not looking for ways to solve problems by negotiations, but is resorting to terror. This is a very worrying thing.”