The extremist group could plant explosives on trains and tunnels or sabotage tracks and electrical cabling, according to the sources.
Bild reported that the information came from the National Security Agency (NSA) in the United States, which had listened in on a conference call involving top Al-Qaeda operatives a few weeks ago.
The attacks on Europe's rail network was a "central topic" of this call, Bild said.
Authorities in Germany have responded to the threat with discrete measures such as deploying plain-clothed police officers at key stations and on main routes.
According to US media reports, intelligence services intercepted a conference call earlier this month between Al-Qaeda leader Ayman al-Zawahiri and more than 20 operatives from across the group's global network.
This prompted the US and several allies to shut embassies across the Muslim
world, fearful of a major attack.
On August 1st, the US issued a worldwide alert, warning of Al-Qaeda plans to
launch an attack in the Middle East or North Africa.
The Local contacted Deutsche Bahn but a spokeswoman declined to comment beyond stating that they work "closely" with the security services.
Meanwhile, Germany's interior ministry said that the security situation regarding terroist threats had "not changed".