BERLIN — Midway through a propaganda video released last month by a group calling itself the German Taliban, a surprise guest made an appearance: a cleanshaven, muscular gunman sporting the alias Abu Ibrahim the American.
The gunman did not speak but wore military fatigues and waved his rifle as subtitles identified him as an American. The video contained a stream of threats against Germany if it did not withdraw its troops from the NATO-led mission in Afghanistan. Although the American's part in the film lasted only a few seconds, it has alarmed German and U.S. intelligence officials, who are still puzzling over his background, his real identity and how he became involved with the terrorist group.
U.S. and European counterterrorism officials say a rising number of Western recruits — including Americans — are traveling to Afghanistan and Pakistan to attend paramilitary training camps. The flow of recruits has continued unabated, officials said, in spite of an intensified campaign over the past year by the CIA to eliminate al-Qaida and Taliban commanders in drone missile attacks.
Since January, at least 30 recruits from Germany have traveled to Pakistan for training, according to German security sources. About 10 people — not necessarily the same individuals — have returned to Germany this year, fueling concerns that fresh plots are in the works against European targets.
"We think this is sufficient to show how serious the threat is," said a senior German counterterrorism official who spoke on the condition of anonymity.
German security services have been on high alert since last month, when groups affiliated with the Taliban and al-Qaida issued several videos warning that an attack on German targets was imminent if the government did not bring home its forces from Afghanistan.
There are about 3,800 German troops in the country, the third-largest NATO contingent after those of the United States and Britain. German officials say Taliban and al-Qaida leaders are trying to exploit domestic opposition in Germany to the war.
Other European countries are also struggling to keep their citizens from going to Pakistan for paramilitary training.
In August, Pakistani officials arrested a group of 12 foreigners headed to North Waziristan, a tribal region near the Afghan border where many of the camps are located. Among those arrested were four Swedes, including Mehdi Ghezali, a former inmate of the U.S. military prison at Guantanamo Bay, Cuba.