No bombs were found on two SAS aircraft after threats were made against an SAS plane late on Wednesday, Belgian prosecutors said, adding that an investigation of a possible terrorist was continuing.

The inspection took place after the prosecutor's office received information about a security threat to an SAS flight .

The prosecutor declined to say how the threats were made. Local media reported they came over Twitter.

Two SAS aircraft that had departed from Oslo and Stockholm were checked for explosives after landing at Brussels-National airport, the prosecutor said in a statement on Thursday.

"This check proved negative," the statement said. "The investigation on the possible threat continues."

Belgium is on alert after Islamist bombers killed 32 people in suicide attacks at Brussels airport and a metro station in March. Many of those who carried out last November's attacks in Paris, which killed 130 people, were based in Belgium. – Reuters