Germany has detained five suspected members of the Islamic State (IS) terrorist group alleged to be planning an attack on U.S. military facilities and an unidentified individual.

Prosecutors said four of the suspects -- all from Tajikistan -- were arrested early on April 15 in the city of Siegen and in the towns of Heinsberg and Werdohl in the western state of North Rhine-Westphalia.

The fifth suspect, also a Tajik national believed to be the leader of the terror cell, was already in custody after being detained in March 2019. The men are all aged between 24 and 32, and came to Germany as refugees.

Federal prosecutors identified the men as Azizjon B., Muhammadali G., Farhodshoh K., Sunatullokh K., and Ravshan B. The suspects' surnames weren't released for privacy reasons.

The men joined IS in January 2019 and were instructed by the terrorist group to form a cell in Germany, prosecutors said.

The suspects reportedly first planned to carry out an attack in their native Tajikistan, but later shifted their target to Germany, including U.S. Air Force bases in the country and a person they deemed critical of Islam.

"Targets for the attacks were supposed to be institutions of U.S. forces in Germany or even individual people," prosecutors said in a statement.

While the attacks were not planned for the immediate future, the group had already acquired firearms and ammunition, as well as secured directions and precursors for making a bomb from the Internet, the statement said.

To help finance the terror plans, prosecutors said the ringleader, Ravshan B., and another suspect traveled to Albania to carry out a $40,000 contract killing, but the operation fell apart and they returned to Germany, the statement added.

The men are alleged to have been in contact with two high-ranking IS figures in Syria and Afghanistan.

Germany's security services estimate there are around 11,000 Islamic radicals in the country, some 680 of whom are deemed particularly dangerous and capable of using violence.

In recent years, Germany has seen several terrorist attacks claimed by IS, including a truck rampage through a Berlin Christmas market in December 2016 that left 12 people dead.

With reporting by AP, Reuters, and dpa