The arrest took place in the middle of the night. In early January, US troops in Afghanistan stormed a house in Kabul and detained 23-year-old Haddid N., according to the Süddeutsche Zeitung on Wednesday. He is now being held at the Bagram Airforce Base on the outskirts of the Afghan capital.

Such arrests, of course, are not an uncommon occurrence in the war-torn country. But Haddid N. is a German citizen. And, despite claims from his family that he was in Kabul to visit his father, officials appear to suspect him of seeking to join the jihad .

The case, though, is sensitive. Haddid N.'s sister, a lawyer in Frankfurt, has accused German security officials of passing on information as to N.'s whereabouts to the US military. She claims that police in Frankfurt questioned her about her brother in early January and asked for the address of Haddid N.'s father in Kabul. Three days later, she said, her brother was arrested.

Lack of Evidence

It wasn't the first time German authorities had shown an interest in Haddid N. He was briefly detained in 2009 before he could board a flight to Pakistan -- to visit his grandmother, he insisted. Officials, though, feared that he planned to travel to a terrorist training camp in the region. For lack of concrete evidence, however, N. was soon released and the case against him was dropped, the Süddeutsche reported. His passport was returned to him last summer.