BERLIN, Nov 5 (Reuters) - German authorities know of up to 50 suspected Islamist militants linked to a trio of Muslims arrested in September on suspicion of planning bomb attacks across Germany, the federal police chief said on Monday.

The plan was foiled in September when police arrested two German converts to Islam and a Turk in the biggest German police operation in 30 years. German police said the trio had trained at what they described as a camp for terrorists in Pakistan.

In a preview of an interview appearing on Tuesday, the head of Germany's BKA federal police, Joerg Ziercke, told Koelner Stadt Anzeiger newspaper that others had also trained in such camps and returned to Germany.

"We believe there are still members of this network in Pakistani training camps," he said.

"Whoever comes back to Germany so radicalised is for us extremely dangerous."

Ziercke said the BKA was still trying to understand the background of the suspected militant network.

"One can assume there are 40 to 50 suspects," he said. "In addition to the leaders are people who were in such close contact with the arrested men that we include them in the network."

The arrested trio, identified by German media as Fritz Gelowicz, Daniel Martin Schneider and Adem Yilmaz, had enough material to make bombs with power equal to 550 kilograms of TNT and were believed to be planning simultaneous car bombs across Germany -- including at facilities frequented by Americans.

Officials have said all three had trained in militant camps in Pakistan before forming a domestic cell of the "Islamic Jihad Union" -- a little known al Qaeda-affiliated Sunni Muslim group with roots in Uzbekistan.

The arrests were the culmination of an investigation that began over a year ago, when U.S. officials alerted German authorities to e-mails intercepted from Pakistan. (Reporting by Louis Charbonneau;)

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