TEHRAN, Iran  — In a square in a poor eastern Tehran neighborhood known for its drug addicts and dealers, psychologist Atefeh Azimi draws another drop of blood from a worried passer-by’s finger.

She works on a nearby bench, where a sign next to her in English and in Farsi urges the public to receive free voluntary counseling and HIV testing.

But her worries, as well as those of her aid group called Reviving Values, are not confined these days just to those sharing needles to inject heroin that comes across the border from Afghanistan’s thriving opium trade.

Iran has seen a surge in the number of HIV infections spread by sex, especially among its youth. What’s more, authorities say many have no idea that they are infected.

That has led to growing uncomfortable questions in the Islamic Republic, where sex outside of marriage is prohibited and those who practice it can face arrest and severe punishment.