A TV report broadcast Wednesday by Swedish private channel SVT accuses Russia of dumping chemical weapons and radioactive waste off the shores of Gotland, a Swedish island in the Baltic Sea.
The toxic material allegedly stems from Russia's Karosta naval base in the Latvian port city of Liepaja, and was unloaded from 1989 until 1992 into the Baltic Sea at night. The report also claims that the Swedish government a few years later learned about the dumping but didn't do anything to locate the waste.
The report relies on intelligence documents and the testimony of Donald Forsberg, a former Swedish military spy, who told SVT he couldn't remain silent any longer.
The nuclear waste affair has shocked Sweden, which is now trying to find out what the former and current governments knew, and when.
Sven Olof Pettersson, an adviser to former Swedish Foreign Minister Anna Lindh, told SVT that Lindh learned what happened and unsuccessfully called for an inquiry into the affair. Lindh was murdered by a mentally unstable man in 2003.
Sweden's Prime Minister Fredrik Reinfeldt has directed calls for an explanation to his predecessor Carl Bildt, who led a Social Democrat government at the time. Bildt, who is now foreign minister, claims he didn't know about the waste dumping.
Russia has so far not commented on the issue. While it would be a severe violation of international conventions, experts say the allegations are not totally unrealistic.
After the Soviet Union collapsed, the Russian military had to quickly abandon its military bases in the Baltics.
"There was lots of war material, no place to store it in Russia, no means for transporting it and no money," Jurik Rakis, a military historian from Latvia, told Austrian newspaper Die Presse.
Either way, the allegations make bleaker the picture painted by experts about the Baltic Sea, considered one of the world's most polluted waters.
Because the Baltic Sea is semi-enclosed, it takes very long for pollutants to be flushed out.
The Soviets dumped their industrial waste into the Baltic Sea, and all major military powers have unloaded their chemical and conventional weapons there since World War I, with an estimated 100,000 tons still sitting on the seabed.
The allegations come less than a week after politicians from nations bordering the Baltic Sea and Russia are due to attend a summit in Helsinki to discuss ways to save this troubled ecosystem.