Police said street children spotted the skull yesterday along with bone fragments while rifling through debris just behind the site of the former Rana Plaza complex in Savar on the outskirts of Dhaka.
"We have recovered the skull and the bones and sent them for tests in the Dhaka Medical College for confirmation if those were really human remains," Savar local police chief Dilip Kumar Saha told AFP.
News of the recovery sparked protests at the site by scores of labour activists and relatives of garment workers still missing in the tragedy last April.
The protesters staged a sit-in at the site, shouting slogans and alleging a cover-up by Bangladeshi authorities.
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Some 3,500 workers were trapped when the nine-storey factory complex imploded in one of the world's worst industrial disasters.
The tragedy highlighted appalling safety conditions for Bangladesh's workers who stitch clothes for poor pay for top Western retailers in the world's second largest garment industry.
Labour activist Taslima Akter said the latest recovery proved that authorities had called off the rescue operation too soon.
"They did a sloppy job and called off the rescue works without recovering all the bodies," said Akter from Bangladesh Garment Workers Solidarity.
"The recoveries are the remains of some of the 158 people who are still missing some 17 months after the tragedy," she told AFP.