Two makeshift grenades exploded outside a building housing the British Consulate in New York yesterday, causing slight damage but no injuries, officials said.

A United Nations analyst found loitering nearby was being questioned, authorities said.

The British Consulate is on the 9th and 10th floors of the 14-storey glass and metal building on the east of midtown Manhattan and about a kilometre from the United Nations headquarters. It has retail shops on the lower level.

"We do not at this point have any idea who did it or a motive," Mayor Michael Bloomberg said, adding the explosion was caused by "a relatively unsophisticated explosive device".

The FBI and police were questioning a United Nations employee from the Netherlands who was found loitering near the building shortly after the explosion, law enforcement officials said.

Officials, including one from the United Nations, confirmed that police had detained and were questioning an analyst with UNMOVIC, the UN commission that was responsible for eliminating Iraq's biological, chemical and long-range missile programmes.

The grenades had been placed inside a cement flower box outside the front door of the building.

In London, a Foreign Office spokeswoman, said: "We're not speculating about whether it's connected to the election."

PHOTO CAPTION

New York police and FBI agents investigate a small explosion that broke a window (background) in the building that houses the British consulate. (AFP)