German authorities have launched a worldwide manhunt for as many as 50 members and supporters of a suspected terror cell that was allegedly plotting to launch multiple car-bomb attacks against U.S. military and other American-related targets in Germany, several officials close to the investigation have told NEWSWEEK.

The plot was first made public when it was foiled a month ago, and three of the group's alleged ringleaders are in custody. But the officials said as many as a dozen active members of the cell are still believed to be on the loose—dispersed to locations including Pakistan and Great Britain. The new information suggests the German terror plot, which heightened security concerns in the United States as well as Europe, involved a more extensive network of Islamic militants than authorities originally disclosed.

Investigators believe five members of the cell, most of them German-born converts to militant Islam, are currently in Pakistan, where they went for training in makeshift camps run by members of the Islamic Jihad Union (IJU), an Uzbek-led affiliate of Al Qaeda's central command. Another two suspects are under surveillance in Germany, according to a German official who, like other investigators, asked for anonymity due to the continuing inquiry. The German-based suspects are being watched while detectives continue to collect evidence that they hope will eventually justify criminal charges.

Yet another suspect, also said to be a German citizen, is believed by German and British authorities to have fled to the United Kingdom. Local authorities are aware of his presence, although it is not clear whether the suspect's precise whereabouts are currently known to investigators. German and British authorities are concerned that the suspect may be trying to get into contact with a possible IJU cell in Britain, though the existence of such a cell has not been confirmed.

German authorities also believe that another 20-30 supporters or helpers of the German-based IJU cell may also be at large; investigators are concerned that a group of sympathizers may have gone to ground in Turkey. Officials also fear that a new leader may have already been designated to replace the plot's suspected mastermind, who was arrested last month. In the last two weeks, Germany's Interior minister, Wolfgang Schaeuble, and other senior German officials have visited the U.S., where they have discussed the IJU case and other terror-related investigations with American counterparts at the Justice Department, FBI, CIA and National Security Agency.

Some German officials have described the IJU case—which culminated in the well-publicized arrests of alleged plot ringleader Fritz Gelowicz and two close associates—as the gravest terrorist threat to face Germany since the end of World War II. (Gelowicz has since been charged with leading a terrorist plot. )