A loud explosion was heard in the Yemeni city of Aden on Thursday evening, residents and a security source told Reuters.
The explosion took place just outside a central prison in the southern port city, they added.
The security source said the explosion happened in an empty area and damaged a wall.
There were no immediate reports of deaths or injuries.
Pictures posted on social media showed a plume of smoke that appeared to rise from an area outside the prison.
After Yemen government officials, backed by Saudi Arabia, arrived in Aden on Dec. 30 at least 22 people were killed in attacks.
*This story was edited by Ahram Online.