British Foreign Secretary William Hague says the U.K. is increasingly concerned there is evidence of that chemical weapons have been used in Syria.

Hague said such allegations must be urgently investigated, telling British lawmakers Monday that those who have ordered the use of such weapons "will be held to account."

He reiterated that no decisions have been made to arm Syrian rebels but stressed that Britain and France are convinced a European Union arms embargo will need to be amended or lifted altogether. The embargo expires at the end of May.

Hague earlier detailed the nonlethal aid Britain has given the Syrian rebels — including five armored 4x4s, 20 sets of body armor, 107 generators and 130 solar-powered batteries — in a written statement to lawmakers.