Prosecutors in Berlin and the neighbouring German state of Brandenburg are interviewing former members of East Germany's secret police, the Stasi, about the 1988 Lockerbie plane bombing, according to officials and media reports.

All 259 people on board and 11 people on the ground were killed when Pan Am Flight 103 blew up over the Scottish town of Lockerbie on its way to New York and Detroit on 21 December, 1988.

Around 20 people, from Berlin and nearby states of Brandenburg and Saxony, have been interviewed.  They are all aged in their 70s and 80s.

Malta has been indelibly yet dubiously linked to the bombing, having supposedly been the place where the bomb was loaded onto feeder flights from Malta by Libyan Abdelbaset al-Megrahi, who was convicted of the bombing in 2001.

He maintained his innocence until death in 2012, and Al-Megrahi's family is now seeking to overturn his murder conviction, citing concerns about the evidence.

In 2001, he had been found guilty of planting the bomb and given a life sentence. He died of cancer in 2012 in Libya after being from Scottish prison on grounds of comnpassion since he was terminally ill, and remains the only person ever convicted for a having a role in the bombing.

In 2003, Libyan dictator Moammar Gaddafi took responsibility for the bombing and paid damages to the victims' relatives.

Berlin prosecutors said on Thursday on Twitter they have received a request for assistance from Scottish authorities "on the basis of which several alleged Stasi employees are questioned, including in Berlin”.

German news agency dpa reported that prosecutors in Frankfurt an der Oder had received similar requests. The ex-Stasi agents are considered possible witnesses, not suspects.

But Bild reported that Scottish prosecutors are investigating whether the Stasi agents may have been part of a plot to bomb the plane, which was ordered by then-Libyan dictator Moammar Gaddafi.

Most of those questioned were members of the Stasi's Department 22, which had contacts with extremist groups in Western Europe, the paper reported.

The prosecutor's office in Frankfurt (Oder) told the dpa news agency that it had received five "European investigation orders." The spokeswoman emphasised that the former Stasi employees were not being treated as suspects.

"These are solely witness interrogations," she said.

According to German daily Bild, which first reported the story, almost 20 former Stasi employees are being sought for questioning in the Lockerbie bombing.