Washington — The U.S. military secretly conducted tests of two deadly chemical weapons in Alberta, according to newly declassified Pentagon documents.

The Pentagon admitted Wednesday that it subjected its own unwitting soldiers to nerve and germ agents during U.S. tests in the 1960s.

Canada, which only recently learned of the tests, said it believes no soldiers were used as guinea pigs during the Alberta exercises.

The tests were conducted in three phases between July 1967 and September 1968 at the Suffield Defence Research Establishment in Ralston, Alta.

They were part of a clandestine operation known only as Program 112 involving chemical and live biological tests in Britain and several U.S. states.

The Alberta tests were used to examine how chemical and biological agents behave in a variety of climatic and environmental conditions. Two agents chemically related to sarin nerve gas were used in the Alberta tests as part of an operation code-named Rapid Tan.

"The purpose of the Rapid Tan tests was to obtain rate-of-vapour return data for agents tabun and soman when sprayed on different terrain types in a summer environment," the documents said.

Former president John F. Kennedy ordered the tests at the height of the Cold War when he was in the White House more than 40 years ago.

Defence Minister John McCallum appeared to have scant knowledge of the covert U.S. military action on Canadian soil.

"We just got this information recently and I'm still looking into it, but my understanding is that this was in the late 1960s, and testing for purposes of defence against biological or chemical weapons took place," Mr. McCallum said Wednesday outside the House of Commons.

"And my understanding also is that no human beings were deliberately exposed to any of these agents."

Tabun vapours as well as soman nerve agents were distributed over the Suffield site using howitzer shells and crop dusters.

Soman is a colourless liquid that can persist in the air for a day, "which gives off an odour of rotting fruit when it vaporizes," the Pentagon document said.

Reactions to soman begin with a runny nose, tightness in the chest, constriction of the pupils and a coma followed by death.

"There is little information available regarding the long-term human health effects of exposure to soman."

Tabun usually kills very quickly. If a lethal does isn't immediately absorbed through the skin, those exposed to the nerve agent are nauseated, go into a coma and suffocate "as a consequence of convulsive spasms."

The Pentagon acknowledged the tests after U.S. veterans who were asked to don protective gear during the exercises began turning up with bizarre illnesses later in life and started asking questions.

Thousands of veterans are only now being made aware of their exposure to VX, sarin and other agents, William Winkenwerder, U.S. assistant defence secretary for health affairs.

"It's not clear that in every instance, people were fully informed" of the risks, Dr. Winkenwerder told a Pentagon news conference.

Congressmen castigated the Pentagon during a committee hearing Wednesday for waiting so long to begin releasing details of the tests.

"It's pretty deplorable that the DOD held this info up for so long," said Congressman Mike Thompson, a California Democrat. "We need to get out there and get these guys tested, and make sure they know the seriousness of what they were exposed to."

Dr. Winkenwerder said there's no evidence anyone died as a result of the classified tests, which were part of biological and chemical warfare programs the United States abandoned in 1970.

Roughly 5,500 service members and civilians participated in the tests, which were kept secret until last year.

Thousands of civilians in Hawaii and Alaska also were likely unaware they were sprayed with relatively mild bacteria meant to simulate germ weapons such as anthrax, Winkenwerder said.