In just over 12 hours after he heard that Russian civilians could be pressed into military service in Ukraine, the young tour guide bought a plane ticket, changed money, bought a laptop, wrapped up his business, kissed his crying mother goodbye and boarded a plane to leave his country, with no idea when he would return.

Thursday morning, he walked into the cavernous arrival hall of the Istanbul International Airport carrying only a backpack and the address of a friend who had promised to put him up while he figured out what to do with his life.

“I was sitting and thinking about what I could die for, and I didn’t see any reason to die for the country,” said the tour guide, 23, who, like others interviewed for this article, declined to give his name for fear of reprisals.

Since President Vladimir V. Putin’s announcement on Wednesday of a new troop call-up, waves of Russian men who had previously thought they were safe from being forced to the front lines have realized they could not count on staying out of their country’s invasion of Ukraine.