Charges that Soviet-backed forces are using toxic gas have appeared in three important areas of Soviet involvement: Afghanistan, Cambodia, and Laos. The latest of the accusations comes from US military officials, who say they have strong but not irrefutable evidence that Soviet forces in Afghanistan may be using, or are about to use, chemical warfare.
Pentagon experts have not pinpointed the exact type of gas used in Afghanistan. "Some form of gaseous agent has been used, but we cannot confirm that it was poison or nerve gas," State Department spokesman Hodding Carter III said recently.
According to some reports, a lethal nerve gas called Soman was spread by bombs dropped by Soviet aircraft in northeast Afghanistan. Although these reports have not been absolutely confirmed, the gas in question causes vomiting, breathing difficulties, and blindness. Other reports indicate that debilitating , but not lethal, gases have been used.
Some refugees from Cambodia have reported Soviet- backed Vietnamese troops used toxic gas against China- backed Khmer Rouge guerrillas.
So far these reports have been extremely sketchy and hard to pin down. But they have gained attention because many Hmong refugees from neighboring Laos have leveled similar charges against Vietnamese and communist Lao forces there.
Earlier allegations that gas had been used in Cambodia had concerned the country's northeast. But last week Thai military sources told newsmen for the first time that Vietnamese-led Cambodia troops are using toxic gas in efforts to clear Cambodia's western border of Khmer Rouge guerrillas.
A military spokesman said the gas -- possibly a type of tear gas -- had been used in a six-day battle for the bridge over the Huei Sa-Lao River. The spokesman said no one was killed by the gas fired from artillery above the stream.
The Khmer Rouge themselves have accused Vietnam of using toxic chemicals and gas in both bombs and mortar shells. According to these charges, the gas produces a burning throat, vomiting, and eventually death. Vietnam has denied using poison gas and toxic chemicals.
Both Lao and Cambodian charges had prompted speculation that the Soviet Union was using these battlegrounds to test its sizable arsenal of chemical weapons.
This speculation surfaced in the case of Laos when refugees of the anti-communist, formerly CIA-supported Hmong army of Gen. Vang Pao initiated gas charges. The allegations covered the period of 1976 to midsummer 1979.
One State Department official concluded, "We do not have absolute proof of these charges. However, the result of US government investigations supports the conclusion that some chemical agent or agents were used in Laos during the period in question. It has been very difficult to obtain physical evidence of poison gas. Some of the symptoms described could possibly result from materials othern than lethal poison gas, e.g. defoliants, riot-control agents, phosphoroous shells, etc."
One problem in confirming the Lao charges was spotty information. A US State Department report on the subject was based on only 20 refugee interviews. No one has produced physical evidence of gas or chemical warfare. And doctors in refugee camps have been reluctant to claim symptoms are specifically from gas.
In the case of Afghanistan, the problem of detection is compounded by the fact that the Soviet divisions are customarily equipped with chemical warfare capability, whether or not than capability is actually to be used. Even if these units are in Afghanistan, further proof is necessary to determine if they are or will be used.
US intelligence is reported to have noted that special TMS 65 trucks equipped to decontaminate soldiers and combat zones are now in Kabul. The presence of highly mobile Frog and Scud missiles able to carry toxic gas has also been reported.