London (AFP) - Three British men overheard talking about "terrorist" activities on a London-bound easyJet flight were released on Sunday after being questioned by German police, the airline said.

The Airbus A319 flying from the Slovenian capital Ljubljana was diverted to Germany's Cologne-Bonn airport on Saturday, causing a major police operation and hours of air traffic chaos.

Passengers on the plane were evacuated using the emergency slides.

The pilot took the decision to divert the plane after passengers told flight attendants "that several men were talking about terrorist activities," a German police spokesman told AFP, without elaborating on the content of their discussion.

The three British men, aged 31, 38 and 48, were taken into custody and authorities said none of them were known to security services.

EasyJet said passengers had stayed overnight in Germany and were flown to Britain on Sunday, while those taken into custody had been released.

"In compliance with the local authorities' guidance passengers disembarked to allow additional security checks to be performed," easyJet said in a statement.

"Three passengers questioned by the police have now been released without charge."

After the plane landed in a secure area of Cologne-Bonn airport at about 6:00 pm (1600 GMT) on Saturday, federal police evacuated the 151 passengers down emergency slides.

They isolated a backpack belonging to the three suspects, which was later blown up outside the plane by bomb squad officers.

The three men were handed over to police who questioned them "on suspicion they planned a serious crime against the state", the term used for terrorist attacks.

Air traffic at the airport was interrupted between 7:00 pm and 10:00 pm with 10 flights diverted and 20 departures delayed.

Cologne police searched the plane using sniffer dogs, but later gave the all-clear.

Germany remains on high alert following several jihadist attacks there and in other European countries.

Authorities the previous weekend evacuated Germany's biggest rock festival, the three-day "Rock am Ring," over fears of a possible terrorist threat, which proved unfounded.