The death toll was expected to rise, said the sources, who asked that they not be identified because they are not authorized to speak to the news media. Two of them work at Republican Hospital in Abyan.

Most of the dead and injured were locals who had been ransacking the factory after it was taken over Sunday by militants, security officials said.

The explosion took place in Abyan Province, they said.

It comes after months of demonstrations against Yemen's President Ali Abdullah Saleh, and a weekend of violence between government forces and the local al Qaeda group.