An additional 150 tiny bone fragments have been recovered from the rooftop of a skyscraper near the World Trade Center site, a spokeswoman for the medical examiner's office said.

The latest remains were recovered at the end of last week, and one more week of recovery work on the roof is planned, Ellen Borakove, spokeswoman for the medical examiner's office, said Monday.

The recovered remains are among thousands still unidentified more than four years after the 2001 attacks. Borakove said they will be tested for DNA with the hope of identifying more victims.

A Sept. 11 family group, unhappy that city officials had not found the remains earlier, has asked the federal government to take over the search efforts. But White House spokesman Alex Conant said the government will let local authorities handle the recovery of remains.

"We've consulted with state and city officials, and they indicate they are proceeding carefully to recover remains, and we have been advised that federal involvement is not requested at this time," Conant said.

More than 500 human bone fragments have been found at the former Deutsche Bank building since workers began cleaning it last fall and preparing to dismantle it. The 41-story building suffered severe damage on Sept. 11, 2001, when the trade center's south tower partially collapsed on it. It has stood vacant since the attacks.

Retired firefighters and fire department battalion chiefs joined in the search last week for human remains that have been found mixed in with gravel on the building's roof.