The measurement of subatomic particles travelling faster than light — contrary to expectations based on Einstein's special theory of relativity — may have been due to a loose cable.

Scientists at an international physics collaboration called OPERA reported last September that they had clocked particles called neutrinos travelling faster than light between the laboratories of CERN, the European Organization for Nuclear Research, near Geneva, and Italy's National Institute of Nuclear Physics, or INFN, in Gran Sasso.

At the time, the researchers said they were surprised by the finding but were unable to trace it to an error. They asked other scientists to scrutinize the results and independently verify the measurements at a different experimental site.

But on Wednesday, ScienceInsider, a blog run by the American Association for the Advancement of Science, said "sources familiar with the experiment" are now blaming the original result on a fibre optic cable connecting a GPS receiver to an electronic card in a computer. The GPS is one of the devices used in the measurement of the neutrino's travel time. The cable connection appeared to have been loose, and tightening it shortened data travel times by 60 nanoseconds.

"Since this time is subtracted from the overall time of flight, it appears to explain the early arrival of the neutrinos," the article said. "New data, however, will be needed to confirm this hypothesis."

CERN spokesman James Gillies confirmed to The Associated Press late Wednesday that a problem in the GPS system used to time the arrival of neutrino particles was discovered earlier in February. He said experiments are being planned for later this year to test whether that introduced an error that made the particles appear to travel faster than light.

The OPERA collaboration had already made some changes to its experimental set up. In November, it announced that even after tweaking the experiment, the particles still appeared to be travelling faster than light.