LONDON (AFP) - Britain said on Wednesday that physiological samples from Syria had tested positive for sarin gas, just one day after France said the same of its own samples, as information grew that the regime was using chemical weapons.

"The material from inside Syria tested positive for sarin," a government spokesman said. "There is a growing body of limited but persuasive information showing that the regime used - and continues to use - chemical weapons, including sarin."

"The room for doubt continues to diminish. This is extremely concerning. Use of chemical weapons is a war crime. Assad must grant immediate and unrestricted access to the UN investigation team."

He said Britain thought chemical weapons use in Syria was "very likely" to have been by President Bashar al-Assad's regime.

"We have obtained physiological samples from inside Syria which have been tested at DSTL," the Defence Science and Technology Laboratory on the government's Porton Down military science park in southern England.

"The material from inside Syria tested positive for sarin. We are not able to go into any further detail on the samples - beyond saying that they are physiological."

The European Union agreed last week to lift its embargo against arming Syrian rebels after tough talks that exposed sharp differences between Britain and France, champions of the move, and their more reluctant partners.