Animal rights extremists are thought to be behind two bombs planted at an Oxford University college.
Security staff at Templeton College in Kennington yesterday discovered the incendiary devices beneath a temporary building during searches sparked by claims on an animal rights website that campaigners had carried out an arson attack there.
The college was evacuated before a bomb disposal unit made the explosives safe.
Forensic officers were seen carrying away four plastic bottles containing liquid for analysis. Police refused to confirm that they were petrol bombs.
The college was on alert after an anonymous posting on the Animal Liberation Front's website on Sunday announced it was responsible for an arson attack seven days earlier in protest against Oxford University's new animal testing laboratory.
The Animal Liberation Front has not officially claimed responsibility for planting the incendiary devices but its spokesman Robin Webb said: "It's probable that the ALF is responsible."
A university spokesman said: "When the university's security services were alerted to the website posting they contacted the college and there was a search of the premises which led to the discovery of the devices.
"We have been vigilant for many weeks. But university buildings must be accessed by students and staff and we cannot make them a fortress."
The anonymous posting made on Sunday on the Bite Back website read: "On the night of Sunday, February 18, the ALF carried out an arson attack on a temporary building of Templeton College at Kennington on the outskirts of Oxford.
"This latest action is part of an ongoing fight against the University of Oxford and its continued reign of terror over the unseen victims inside its animal labs."
The university said there was no attack on February 18.
She added that the temporary buildings where the bombs were found were not used for teaching purposes.
Police officers at the scene would not confirm what the explosives were, but said there was no link to letter bombs sent to businesses in Abingdon and Culham earlier this year.
Forensics teams removed four large plastic bottles containing a yellow-brown liquid.
Officers from Operation Rumble, which investigates animal rights attacks, are involved.
Police spokeswoman Rachel McQuilliam added: "At this stage it is too early to say if animal rights campaigners are responsible, but the posting on the website will form part of our inquiry."
Abul Kashem, 64, whose home in Upper Road backs on to the college site, said: "I'm really worried as we are quite close, and if they put a bomb somewhere in the college it could be close to the back of our garden."
Templeton College is the specialist graduate college for students reading for postgraduate degrees in management and business studies. The college is also the home of the Said Business School's executive education facility.