"The security services have done a very good job and I can't say anything more at this point," he said. 

  

Targets

 

Frankfurt international airport is one of Europe's busiest and the Ramstein base in the nearby state of Rhineland-Palatinate, 130km southwest of the airport, is one of the most important US air bases overseas.

 

Ramstein is a crucial transit point for US military operations in Iraq and Afghanistan.

   

Germany, which has forces stationed in Afghanistan, has been on high alert for attacks.

 

The country has feared a re-emergence of Islamic groups since 2001, when the northern port city of Hamburg was used as a base for the September 11 attacks in the United States.

  

Earlier this year, federal prosecutors charged a Lebanese man held in detention over an unsuccessful attempt to detonate bombs on two trains in Germany in 2006.