The official, who spoke on the condition he not be named because of the sensitive nature of the issue, said he could not confirm press reports that the accident killed at least 40 al Qaeda operatives, but he said the mishap led the militant group to shut down a base in the mountains of Tizi Ouzou province in eastern Algeria.
He said authorities in the first week of January intercepted an urgent communication between the leadership of al Qaeda in the Land of the Maghreb (AQIM) and al Qaeda's leadership in the tribal region of Pakistan on the border with Afghanistan. The communication suggested that an area sealed to prevent leakage of a biological or chemical substance had been breached, according to the official.
"We don't know if this is biological or chemical," the official said.
The story was first reported by the British tabloid the Sun, which said the al Qaeda operatives died after being infected with a strain of bubonic plague, the disease that killed a third of Europe's population in the 14th century. But the intelligence official dismissed that claim.
AQIM, according to U.S. intelligence estimates, maintains about a dozen bases in Algeria, where the group has waged a terrorist campaign against government forces and civilians. In 2006, the group claimed responsibility for an attack on foreign contractors. In 2007, the group said it bombed U.N. headquarters in Algiers, an attack that killed 41 people.
Al Qaeda is believed by U.S. and Western experts to have been pursuing biological weapons since at least the late 1990s. A 2005 report on unconventional weapons drafted by a commission led by former Sen. Charles Robb, Virginia Democrat, and federal appeals court Judge Laurence Silberman concluded that al Qaeda's biological weapons program "was extensive, well organized and operated two years before the Sept. 11" terror attacks in the U.S.
Another report from the Commission on the Prevention of Weapons of Mass Destruction Proliferation, released in December, warned that "terrorists are more likely to be able to obtain and use a biological weapon than a nuclear weapon."
British authorities in January 2003 arrested seven men they accused of producing a poison from castor beans known as ricin. British officials said one of the suspects had visited an al Qaeda training camp. In the investigation into the case, British authorities found an undated al Qaeda manual on assassinations with a recipe for making the poison.
The late leader of al Qaeda in Iraq, Abu Musab Zarqawi, was suspected of developing ricin in northern Iraq. Then-Secretary of State Colin L. Powell referred to the poison in his presentation to the U.N. Security Council in February 2003 that sought to lay the groundwork for the U.S. invasion of Iraq.
Roger Cressey, a former senior counterterrorism official at the National Security Council under Presidents Bill Clinton and George W. Bush, told The Washington Times that al Qaeda has had an interest in acquiring a poisons capability since the late 1990s.
"This is something that al Qaeda still aspires to do, and the infrastructure to develop it does not have to be that sophisticated," he said.
Mr. Cressey added that he also is concerned about al Qaeda in the Land of the Maghreb, which refers to the North African countries of Algeria, Morocco and Tunisia.
"Al Qaeda in the Maghreb is probably the most operationally capable affiliate in the organization right now," he said.