(Adds report about suspect's link to nuclear facility)

By Sabine Siebold and Iain Rogers

BERLIN, June 22 (Reuters) - German authorities called on Friday for increased vigilance against possible terror attacks and said the kind of threat detected before the Sept. 11, 2001, suicide hijackings in the United States had resurfaced.

Interior Minister Wolfgang Schaeuble said the threat was "serious" and suicide attacks were possible on German soil.

The present situation recalled the summer of 2001 "when obscure threats surfaced which, as we know, became reality", said Deputy Interior Minister August Hanning.

"We are seeing evidence that some action is planned in (the Afghanistan and Pakistan region) but also further afield, in Europe and in the United States," Hanning said in Berlin.

"We are following up all leads and therefore I don't think there is any reason to panic, not at all. But I do think that increased vigilance is needed."

Interior Ministry spokesman Christian Sachs said earlier there was evidence to suggest terrorist training groups in Afghanistan had become stronger and were ready for action.

People from Europe, including Germany, were part of these groups.

German state broadcaster ZDF had reported on Friday that the government had evidence 10 to 12 people from Germany were in militant training camps in Afghanistan and Pakistan.

Three of them, including two people considered dangerous, were arrested in Pakistan as they attempted to travel back to Germany, ZDF said.

German newspaper Sueddeutsche Zeitung reported that one of the three had worked for an engineering firm that had access in the past to a nuclear research reactor facility in Karlsruhe.

Prior to his arrest German authorities had labelled the 45-year-old naturalised German citizen "dangerous", the paper said citing unnamed sources.

Joerg Ziercke, the head of the federal crime office (BKA), said on Friday the authorities were aware of 10 German militants who had joined training camps in Pakistan.

Three of them had been arrested on the basis of a video obtained by U.S. broadcaster ABC, Ziercke said. The other seven were still in Pakistan.

ZDF said the video contained threats targeted at Germany. "We are concerned and worried and also alarmed," Ziercke said at a news conference in Wiesbaden.

German government spokesman Thomas Steg said there was no concrete danger and people should carry on as normal. (Additional reporting by Catherine Hornby and Bernhard Winkler)

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