UN officials said on Thursday there was no danger to staff or members of the public.
The canisters were removed from the premises by the FBI and New York police hours later and taken to the US Army laboratory in Maryland.
|The chemical was recovered from an Iraqi |
weapons facility 10 years ago [GALLO/GETTY]
The material was discovered last Friday, but it was only on Wednesday that inspectors found an inventory list which identified the substance as phosgene, a choking potentially lethal chemical warfare agent used extensively during World War One.
The substance was recovered in 1996 from a former Iraqi chemical weapons facility, al-Muthanna, north of Baghdad.
The Security Council disbanded UNMOVIC on June 29 this year and the offices were being cleared for closure when inspectors discovered the canisters.
Ewen Buchanan, a UNMOVIC spokesman, said UN experts believe "the packages are properly secured and pose no immediate risk or danger to the immediate public".
The materials were isolated in a secured room and no toxic vapours had escaped, he added.
Buchanan, in whose offices the material was found, said inspectors found two small plastic packages with metal and glass containers, and small vials and tubes the length of a pen with liquid inside.
He said the canisters "should not have come here" because such material is normally taken to a secure laboratory.
Marie Okabe, a UN spokeswoman, said the UN secretary-general had been informed and "there will be an investigation".
Saddam Hussein evicted UN inspectors searching for weapons of mass destruction from Iraq in 1998.
They returned in early 2002, but was ordered to leave by the US shortly before the March 2003 invasion.