An Afghan father in the northern city of Kunduz has handed over his teenaged son to police after becoming worried he might have been groomed to become a suicide bomber.
The father told the BBC he had been worried about his son for some time.
He said he panicked on hearing of a suicide attack in the city on Saturday.
At least 10 police were killed in the attack on a crowded market, including the city's head of counter-terrorism and another high ranking officer.
Police spokesman Sayed Sarwar Husseini told a press conference on Tuesday that the father's actions had "prevented another bloody attack and lethal casualties".
The father cannot be named to protect his family's identity.
"I was in the shop when I heard there was a suicide attack, and I was worried it could have been carried out by my second son," he said.
The father rushed home, but initially could not find the youth before finally tracking him down at a house in the city.
When the men who were with his son refused to let him come home - saying they would send him back the next day - the father made the decision to call the police and give them the address.
The father said that he did so because he feared the 16-year-old might have been radicalised.
Police later raided the house and arrested the youth and another person.
They told the BBC that they believed the house where the arrests were made was rented by people who had been "preparing suicide attackers", although no bomb-making material was found.
The father told the BBC that the family returned to Kunduz late last year after living in Pakistan for 30 years.
He said that his son had "completely changed" after disappearing without trace for several months before their departure.
When he re-joined the family, he had become "very withdrawn", the father said.
He said that his son had received religious instruction and had begun to read the Koran avidly.
"I was worried about his behaviour," the father said. "He told us that he was with Pakistanis and that they were regularly giving him medicine."
The father became so worried that he decided to leave Pakistan. But even in Kunduz, he says, his son continued contacting Pakistani men.
The youth is now in police custody - his father says that he will now go through a re-education programme.
Correspondents say that the father is being hailed by the authorities as an example of how ordinary people can help to counter youth radicalisation.