Fourteen years after Switzerland's worst-ever environmental disaster, the authorities are considering reopening their investigation into what caused the blaze at a chemicals factory near Basel.
The move follows new information suggesting the fire at the Sandoz chemical works could have been started deliberately by agents of the former East German security service (Stasi).
The claims of sabotage were made by a former senior CIA official and reported on German television's "History" programme on Sunday.
The CIA official, Vincent Cannistraro, told the programme the Stasi agents were acting on the orders of the KGB. He said a former KGB officer told him the motive was to divert attention from the Chernobyl nuclear disaster, which had occurred six months earlier.
Fire broke out at the factory at Schweizerhalle in Arlesheim on November 1, 1986. Some 1,351 tonnes of chemicals went up in flames, releasing a toxic cloud over Basel and poisoning the Rhine river.
The cause of the blaze was never established. The judicial authorities in canton Basel Country say they are examining the allegations to decide whether to reopen the enquiry into the disaster.
"We are examining these reports," the interim governor of Arlesheim said. "But that does not mean that the Schweizerhalle file will be reopened."
swissinfo with agencies