German Interior Minister Thomas de Maiziere said on Wednesday that he could not yet confirm reports that eight German militant Islamists had been killed by a US drone attack at the start of the week, DPA reported.
"I am very surprised that this attack allegedly took place the day before yesterday, in an inaccessible area, by unmanned drones, and, at the same time, identification documents were found," de Maiziere said in a radio interview.
"Not all of this make sense. We still need to clarify things," the minister told Deutschlandfunk radio.
In recent days, de Maiziere has stressed that Germany faces no increased danger of imminent attacks by militant Islamists. In the interview, he added that such a threat was "hypothetical."
However, the minister said there were "several indications" from independent sources about extremist activity in the Pakistani border region, adding that an increasing number of people were travelling between Germany and the area.
"We don't know all of them, we know many of them. We have also prevented much of this travel. Some return frustrated, some return trained - whatever that means. We have an eye on all this," the minister said.
Late Monday, a pilotless US aircraft fired two missiles at a house in Pakistan's tribal region along the Afghan border. Of the eight people reported killed, five were allegedly German converts to Islam and three were identified locally as Germans of Turkish origin.
The German Foreign Ministry has so far declined to comment on the attack, stressing that they had "no reliable information" on Monday's events.