DUBAI, Jan 19 (Reuters) - Egypt's blue-chip stock index tumbled 3.4 percent by the early afternoon on Thursday after Reuters reported that authorities were considering temporarily reintroducing a stamp duty on stock market transactions.

"We are studying temporarily re-imposing a stamp duty on stock market transactions pending the return to a capital gains tax, which has been postponed since May 2015," one of the sources said, speaking on condition of anonymity.

All but three of the 30 shares in the index were sold with Ezz Steel slumping its 10 percent daily limit. The broader EGX100 index was down 2.9 percent.