"The guards from Aden central prison foiled an escape attempt with the discovery of an eight metre (yard) long tunnel dug by the 25 detainees," the official told AFP.

"Another two metres and the tunnel would have reached a market near the prison" in the Mansura district of Yemen's main southern city, he added.

The detainees included "some dangerous elements who were to be transferred to Sanaa," the official said.

Aden prison houses many suspected or convicted members of Al-Qaeda which has been particularly active in the south and southeast of Yemen.

In December last year, 12 Al-Qaeda prisoners escaped from the jail, just months after 60 escaped from a prison in the port of Mukalla, killing a guard.

In June this year, five Al-Qaeda prisoners broke out of a jail in Hodeida on the Red Sea coast.