Armed men are reported to have taken control of a provincial capital in the unsettled south of Yemen.
Government officials and residents said fighters from al-Qaeda in the Arabian Peninsula (AQAP) were among those who seized Zinjibar, in Abyan province.
But opponents said President Ali Abdullah Saleh had given up the town to stoke fears of a militant takeover.
He is resisting calls to step down, despite months of popular protests and growing opposition from a key tribe.
At least 124 people died in recent days in the capital, Sanaa, in clashes between government forces and fighters loyal to Hashid tribal leader Sheikh Sadiq al-Ahmar.
A ceasefire was eventually agreed on Saturday and a deal reached to withdraw troops from Sanaa, though the timing remains unclear.
Official reports emerging from Zinjibar suggested the town was seized by force.
The AFP news agency reported that 16 people had been killed during Friday and Saturday during fighting in and around Zinjibar.
But other reports made no mention of violence. One resident of Abyan province told the BBC that the town was chaotic and there was widespread looting.
"About 300 Islamic millitants and Al Qaeda men came into Zinjibar and took over everything on Friday," a Zinjibar resident told Reuters.
However, one military unit was reported to have refused to surrender and was now surrounded, reports said.
There are conflicting accounts of the loyalties of the armed men, reflecting the complex nature of military loyalties in Yemen.
While government officials said the men were AQAP, one analyst told the BBC they were in fact an older, more established group of fighters loyal to President Saleh and his now-rival, the defected army officer Ali Mohsen (who is also Mr Saleh's brother-in-law).
The government has blamed previous attacks in southern Yemen on al-Qaeda, but the country's opposition has accused President Saleh of stoking fears of an Islamist takeover.
That pattern was quickly repeated as news emerged from Zinjibar. Opponents accused the president of allowing the town to fall to the armed men in order to claim that AQAP were becoming a major threat to Yemen's stability, the AFP news agency reported.
AQAP is known to be active in southern Yemen, but the region is also home to a long-running separatist insurgency.
The group is described by the US as one of the world's most active al-Qaeda cells.
However, it usually operates from mountainous areas away from towns and cities.
Yemen is beset by problems, including dwindling oil supplies and a growing water crisis as well as grinding poverty, political unrest and the presence of al-Qaeda and separatist rebels in the south.