BERLIN — I met Mori in the basement of a Lutheran church in Berlin’s Zehlendorf district. A 28-year-old refugee who once ran a small business in Iran, he converted to Christianity five years ago and spoke to me on condition that I use only his first name in order to protect his identity. In 2011, delayed on the way to a secret Bible study session, he narrowly escaped when Revolutionary Guards raided his underground Evangelical church. He watched as his friends disappeared into Iran’s prison system; Mori suspects they’ve been killed.

“When you’re Christian in Iran, you can’t speak. You have to keep quiet and not talk about the truth that you know and that you believe in,” he told me. “There is no such thing as a comfortable life in Iran.”

Christianity of course is not alien to Iran. It arrived in ancient Persia not long after the death of Christ and has waxed and waned ever since. But in recent decades, especially in the last few years, things have grown worse. As Washington seeks rapprochement with Tehran over Iran’s nuclear and regional ambitions, the Obama administration must not let its protests over cruel treatment of Christians and other religious minorities fall by the wayside.

Christians make up roughly less than half of 1 percent of Iran’s roughly 80 million people. Numbers are difficult to determine: There could be as many as half a million Christians in the country, according to a report by the International Campaign for Human Rights in Iran. It cites research by the World Christian Database indicating that there were 270,000 living there in 2010. Most of them are ethnic Armenians and Assyrians who, though closely monitored, are able to practice their own Orthodox faith. It is the other denominations — mostly converts from Islam to Evangelical Protestantism — that are more likely to be harassed, imprisoned or even murdered.