Updated

New York City Mayor Michael Bloomberg said Monday there is no reason for anyone to be embarrassed by the discovery of more remains believed to belong to victims of the Sept. 11 World Trade Center attacks.

Bloomberg's comments come a day after 18 new pieces were found, and officials said they have yet to unearth more than half the underground sites apparently overlooked during the initial search for human remains in the area of the attacks. The new finds added to a total cache ranging from tiny fragments to recognizable bones from skulls, torsos, feet and hands, the medical examiner's office said.

Families of the 2,749 victims, 40 percent of whom still have no identifiable remains, have been outraged by the horrific discovery of the underground tombs where the bones and fragments were found. They are calling for federal intervention, have demanded answers about why the search was incomplete and want construction halted until the recovery is complete.

But Bloomberg reiterated Monday that construction at the site would not stop and said the city has "every reason to be phenomenally proud" of those who carried out the recover, where nearly 20,000 pieces of human remains were recovered.

"There's no reason for anybody to be embarrassed — it was a very big job. And just the reality of it is, there will always be more places you could have gone," he said.

Deputy Mayor Ed Skyler, who is overseeing the recovery effort, said Sunday that search officials had identified additional manholes and utility cavities that need to be examined.

The team of searchers, which includes police and fire officials and forensic anthropologists from the medical examiner's office, expects to burrow into at least 12 subterranean areas in coming days. About five have been excavated.

"They will go through every grain, every piece of material carefully, and sift through it," Skyler said.

The underground pockets are located along the western edge of the 16-acre lower Manhattan site, underneath a service road that was built in March of 2002 as the excavation was ongoing.

When the service road was built, some below-ground cavities that had been used for utility and infrastructure purposes were paved over without being searched for remains. Days ago, crews doing routine work at the site opened one of those manholes and discovered human bones inside, setting off an expedition for other remains.

Skyler said the city is focused on finding remains before it will turn to a review of any missteps.

"It's a question that should be answered, but for now our focus is on dealing with the situation and finding whatever remains are recoverable," he said.