Swedish furniture giant Ikea on Friday admitted that some of its suppliers used forced labour in former Communist East Germany and expressed "deep regret" that its controls were less strict at the time.

Releasing a report into the use of forced labour in East Germany that came under fire even before it was published, Ikea said there were "indications that political prisoners and convicts were partly involved in producing parts or pieces of furniture that were delivered to Ikea 25 or 30 years ago."

"In addition, the investigation showed there were Ikea managers who were aware of the possibility that political prisoners would be used to manufacture Ikea products in the former East Germany," added the report by auditors Ernst and Young.

While the firm took steps to ensure this did not occur, "it is now clear that these measures were not effective enough," the furniture giant acknowledged.

"At the time, we did not yet have the well-organised control system we have today and clearly did not do enough to prevent this type of production method," the firm said.

The Ernst and Young report examined around 20,000 documents from the Ikea archives between 1960 and 1990 as well as some 80,000 pieces of evidence from the German historical files.

The auditors also carried out some 90 interviews with a variety of Ikea employees, as well as with prisoners and witnesses.

"We deeply regret that this could happen," said Jeanette Skjelmose, sustainability manager at Ikea.

"The use of political prisoners in production has not been accepted at any time," she added.

But the report itself came under attack even before its publication.

Klaus Schroeder, a political scientist at Berlin's Free University, said: "It would have been simpler to come and ask us because we are the experts on this subject."

Roland Schulz, vice-president of an association representing victims of the Communist regime in East Germany, dismissed the report as "unscientific."

"Ikea as the guilty party is itself conducting the investigation rather than leaving it to unbiased sources. Therefore we strongly doubt the validity of the results," he added.

He called for historians and political scientists to carry out a more thorough investigation.

According to media reports, Ikea was far from being the only company to employ forced labour in the former Communist East, noting that the mail-order companies Neckermann et Quelle are also alleged to have observed similar practices.

But Rainer Wagner, the president of the UOKG group representing "victims of communist tyranny" told the Berliner Zeitung daily on Friday that Ikea's efforts were "a start" and called on other firms to investigate their past.

The UOKG and other victims' groups have called for a compensation fund to be set up for former forced workers under the East German communist regime.