The Obama administration is concerned that a dangerous regional arm of al Qaeda is trying to produce the deadly poison ricin to use in attacks against the United States, the New York Times reported.
Citing unnamed intelligence officials and classified intelligence reports, the newspaper said al Qaeda's affiliate in Yemen has been trying to acquire large quantities of castor beans, used to produce ricin.
It said the apparent intent was to pack the poison around small explosives that could be exploded to disperse the ricin, a white powdery substance so deadly that a speck can kill if inhaled or taken into the bloodstream.
The Times said the apparent intent was to detonate the explosives in enclosed spaces like a shopping mall or airport.
US President Barack Obama and top security aides were briefed about the threat last year, the report said, and have received updates since then but added that senior American officials said there was no indication an attack was imminent.
The Times noted that there were limits on ricin's utility as a weapon because it loses its potency in dry, sunny conditions -- like those in Yemen -- and is not easily absorbed through the skin like some other nerve agents.
Senior administration officials said ricin was among the threats being tracked by a secret government task force created after printer cartridges packed with powerful explosives were found in cargo bound for Chicago in October 2010, according to the Times report.
It said the task force was working with Saudi officials and with the remnants of Yemen's intelligence agencies to counter the threat. It said regional al Qaeda affiliates, especially al Qaeda in the Arabian Peninsula, were seen as a menace to the United States and U.S. interests abroad.
The virtual collapse of Yemen's government has enabled al Qaeda to widen its control in the country and strengthen its operational ties with al Shabab, the Islamic militancy in Somalia, the Times said.