REUTERS - A staff member from the French embassy in Tehran who is on trial for spying has been released from jail although she is still being prosecuted, a statement from President Nicolas Sarkozy's office said on Tuesday.

Nazak Afshar, who works at the cultural section of the embassy, is among dozens of defendants at a mass trial, along with French teaching assistant Clotilde Reiss.

The women are charged with espionage and taking part in a Western plot to overthrow the government. France has dismissed the charges as baseless.

"The president has learnt with great joy and relief of the release from prison of Mrs Nazak Afshar," a statement from Sarkozy's office said. He called for charges against her to be dropped and for Reiss also to be freed and returned to France.

Iran is conducting mass trials aimed at uprooting the opposition and putting an end to protests that erupted after disputed June 12 presidential election.

Afshar's release came after intense diplomatic activity and conflicting statements from French and Iranian officials about Reiss.

The Iranian ambassador to France, Seyed Mehdi Miraboutalebi, said on Tuesday that Tehran had offered to let Reiss stay in the French embassy during her trial on certain conditions but that there had been no answer from Paris.

The French foreign ministry swiftly denied this, saying the ambassador had been summoned to explain himself.

"He was told that his comments suggesting that the French authorities were not doing everything they could to obtain the release of Clotilde Reiss were erroneous," the ministry said.

"He was probably ill informed. We refute them categorically."

The ministry added that it had been telling the Iranian authorities for several weeks that it was prepared to host Reiss at the embassy should she be granted conditional freedom during their trial, but that this had yet to happen.

Government spokesman Luc Chatel had said earlier on Tuesday that authorities were hopeful that Reiss would soon be freed.

Miraboutalebi, speaking on French radio station RFI, said Tehran had proposed that Reiss be freed from prison and stay at the French embassy during her trial, on condition that the French government commit itself to keeping her there.

"So far we have had no reply from the French ambassador," he said.

The envoy also said that France had been told before the trial not to publicise Reiss's case in the media, or "we will not be able to do anything any more because, as in France, the Iranian judiciary is totally independent".

A solution could have been found "calmly", but the French ignored the advice and were to blame for Reiss's predicament, the ambassador said.

"Unfortunately, our French friends did not have the necessary patience and they claimed that this young lady was totally innocent. In other words, they took the place of the Iranian judges," he said.