The police were commenting on a report in the German news magazine Focus, which spoke of planned suicide bombings at German installations in Afghanistan, where Germany has around 3,500 troops stationed as part of a NATO-led peacekeeping mission.

While police confirmed that they had issued warnings about possible attacks, they declined to comment on details in the news article.

"We have warned our national and international partners, and possibly endangered institutions, of terrorist activities by two people from the German Islamist spectrum," a BKA spokesman told Reuters.

Focus reported on its Web site on Thursday that a 20-year-old German national, identified as Eric B., was thought to have links to the three men arrested in Germany last year who allegedly planned attacks on US installations in Germany. It also reported that besides the German, an Egyptian national was also involved.

Picture distributed

The magazine reported that the BKA, along with its warnings, sent a picture of Eric B. to the German embassy in Kabul. His photo has also been posted at German organizations in Afghanistan.

Officials are particularly worried that since Eric B. speaks fluent German, he could win the confidence of German troops or groups in Afghanistan. According to the magazine, his apparent targets were soldiers or policemen, although civilian organizations are also thought to be at risk.

Last month, a video surfaced apparently showing Germany's first Muslim suicide bomber in Afghanistan.

Cüneyt Ciftci, a 28-year-old man of Turkish descent who was born in Bavaria, blew himself up outside a government building in Afghanistan, killing two US soldiers and two Afghanis.

BKA chief Joerg Ziercke said the video risked radicalizing Islamists in Germany.