Residents are becoming fearful of a possible attempt by Islamic militants to seize control of the strategic port city.
The Yemeni government said it suspected al-Qaeda was behind the bombing on Friday in Aden's free-trade zone. The bomb went off after anti-government demonstrators in the city and across the nation again held large weekend rallies in their four-month campaign to oust Yemen's autocratic leader of nearly 33 years.
Regime opponents have accused the government of exaggerating the al-Qaeda threat to try to hang on to Western support. Investigators said it was too early to tell what caused the blast.
The months of political turmoil have raised fears, perhaps most acutely in the US, that Yemen's al-Qaeda franchise will seize the opportunity and carve out more room to operate freely and plot attacks on the West from its bases in the country's remote and mountainous hinterlands.
Residents of Aden said their worries of a possible militant takeover were fuelled by the sudden and unexplained withdrawal of military forces loyal to embattled President Ali Abdullah Saleh from checkpoints at the entrances to the city and other key positions.
A similar government withdrawal preceded the recent takeover of two nearby towns by hundreds of Islamic militants, some of them thought to be linked to al-Qaeda in the Arabian Peninsula.
"We are all very worried of what lies ahead. There are rumours all over the town that militants from al-Qaeda will take over Aden," said Mohammed al-Dalei, a 28-year-old teacher.
Some residents said gunmen appeared around Aden in recent days, sometimes firing randomly in the air or at strategic buildings, such as the Central Bank.