Three persons suspected of planning a series of bomb attacks targeting the Frankfurt Airport and the US military airbase at Ramstein have been arrested by German security forces, officials said Wednesday.

The German Defence Minister Franz Josef Jung confirmed the arrests and said, “There was an immediate threat.”

According to the federal prosecutors office in Karlsruhe, the suspects were arrested Tuesday afternoon and a massive search operation was launched in several German states.

Federal Prosecutor-General Monika Harms said two German men converted to Islam and a Turkish Muslim were detained in Oberschledorn, a small town in the western state of North Rhine-Westphalia.

Harms told journalists the three were part of a terrorist organization named the Islamic Jihad Union, which was formed in Uzbekistan. The suspects have been allegedly trained in Pakistan.

The director of Germany’s Federal Criminal Police Office (BKA) Joerg Ziercke said the men were being monitored for several months and the terrorist cell they were part of has connections with al-Qaeda.

Ziercke said members of the counter-terrorism unit of the German Federal Police (GSG 9) moved in after reports indicated the suspects began manufacturing a bomb and were preparing to move their illegal workshop.

One of the men managed to flee the house, but was quickly detained by security forces that cordoned off the area. Ziercke said the alleged terrorist tried to seize a weapon from one of the policemen and a shot might have been fired during the scuffle, but further details remained unclear.

Investigators found a dozen containers with 730 kilos of hydrogen peroxide inside, the same substance used to fabricate the bombs detonated two years ago in London. But the quantity found by German police could have been transformed in a larger amount of explosive substance, specialists estimating it could have had the destructive force of 550 kilos of TNT.

Preliminary investigations revealed that a series of car bombs were going to be detonated near the US military base. The air base is located in the German state of Rheinland-Pfalz, at about 16 kilometers (10 miles) from Kaiserslautern. Several small communities surround the base which is an important transit point for US aircrafts heading for the Middle East.

The Ramstein Air Base is one of the largest military facilities of the United States in Europe, but army officials at Ramstein couldn’t confirm the report of a potential terrorist attack targeting the facility.

Also on Tuesday, Danish police detained eight men believed to be planning a large scale terrorist attack. Investigators said two had ties with al-Qaeda and appeared in front of a court, while the six others have been released.