MENA said the fight late on Monday started when a shop owner opened fire with his automatic rifle and killed two people who spread their merchandise on the ground outside his shop.
The agency said colleagues of the two set fire to the man's shop, where he and 12 of his workers were taking cover, killing them all.
The gunfight and the revenge arson in the old Cairo neighbourhood of el-Moski are the latest signs of lawlessness that has struck Egypt during two years of political turmoil.
COMMENT RULES: Comments that are judged to be defamatory, abusive or in bad taste are not acceptable and contributors who consistently fall below certain criteria will be permanently blacklisted. The moderator will not enter into debate with individual contributors and the moderator’s decision is final. It is Belfast Telegraph policy to close comments on court cases, tribunals and active legal investigations. We may also close comments on articles which are being targeted for abuse. Problems with commenting? email@example.com