The developments came as Shiite rebels known as Houthis launched new attacks, after weeks of retreating as pro-government troops pushed north out of Aden. Yemen's fighting, which escalated in March, pits the Houthis and troops loyal to former President Ali Abdullah Saleh against southern separatists, local and tribal militias, Sunni Islamic militants and troops loyal to President Abed Rabbo Mansour Hadi.
Thursday's explosion in Gov. Nayef al-Bakry's office also wounded 10 people, local police officials said. Al-Bakry, who oversees the Aden governorate, was in the building at the time, meeting with high-profile military and security officials.
No one claimed responsibility for the attack and authorities were investigating, said the officials, speaking on condition of anonymity under regulations.
Backed by a Saudi-led coalition that started carrying out airstrikes against the rebels in March, pro-government fighters took Aden in July, after driving out the Houthis who had seized it in the spring.
In Taiz, Yemen's third largest city, at least 11 civilians were killed and more than 35 injured by shelling that started on Wednesday, independent local officials, witnesses and medical officials said, speaking on condition of anonymity because they were not authorized to talk to reporters.
They all said the shelling was by Houthi fighters who were attacking areas controlled by pro-government forces. Houthi reinforcements were being sent to the city, witnesses said. Anti-rebel fighters had captured several locations in Taiz over the past week, and currently control most of the city.
Meanwhile, Islamic State-affiliated militants claimed an attack Wednesday that killed a Yemeni soldier at a checkpoint in Hadramawt province. The Associated Press could not independently verify the claim, which was posted by IS sympathizers on Twitter Thursday.
Initially, Yemen's al-Qaeda branch was suspected in the attack.