The search was prompted by the discovery on Friday of about 80 human bones and fragments in rubble from an abandoned manhole near the site.

It sparked angry calls from victims' relatives for a more thorough search.

Families of more than 1,100 of those who died have never received any remains of their loved ones.

After construction workers made the first unexpected discovery on Friday, city officials then ordered new checks of underground areas close to Ground Zero that could have been missed.

On Saturday, workers removed more debris from manholes. Forensic officials sifted it and found another 15 human fragments, Deputy Mayor Edward Skyler said.

More manholes will be searched in coming days, officials said.

The original search of the site ended in 2002, after about 20,000 human fragments had been unearthed.

The discovery comes just weeks after the fifth anniversary of the 11 September 2001 attacks, in which more than 2,700 people died.