Iran on Tuesday accused two German journalists of spying after they were arrested interviewing the son of a woman condemned to death by stoning, stirring fresh tension with the West ahead of nuclear talks.

"These two Germans came to Iran claiming to be tourists," said Malek Ajdar Sharifi, justice department chief of East Azerbaijan province in the northwest of the country where the arrests were made, quoted by Fars news agency.

"But the work of these two tourists in Iran and Tabriz and the way they reported in Tabriz show that they came for espionage," he said.

"In fact these two came here for espionage and, thank God, they were identified and arrested ... The evidence for espionage was in their hands when arrested and they were planning a smear campaign against the Islamic republic."

The development came as the foreign ministry in Tehran said Iran and world powers, including Germany, had yet to agree on the venue and agenda for a resumption of nuclear talks planned for December 5.

"The consultations are ongoing," foreign ministry spokesman Ramin Mehmanparast said. "We have reached an agreement on the date. For the rest, once there is an agreement we will announce it."

On Monday, Iranian state-run television showed blurred footage of the two as yet unidentified German men "confessing" that they had been "tricked" into travelling to Iran.

According to the Farsi voiceover of the footage, the journalists arrested on October 10 pointed fingers at Mina Ahadi, an Iranian human rights activist living in exile in Germany.

Ahadi, founder of the Germany-based International Committees against Execution and Stoning, has launched a global campaign to halt the impending execution of Mohammadi-Ashtiani by stoning.

"I did not have any information about this case, but Ms Ahadi knew about it. She sent me to Iran and has gained propaganda value from my arrest. I will sue Ms Ahadi when I am back in Germany," one of the detainees was quoted as saying.

"I accept that I made a mistake. Since I had no information on the case, I was tricked by Ms Ahadi," the other German was quoted as saying.

In Germany, Ahadi hit back on Tuesday, telling AFP: "I did not send them to Iran. I spoke to them about the risks and helped them make contacts.

"I do not think the journalists were mistreated physically ... But they were certainly under psychological pressure," said the activist.

"They have been in prison for a month ... no contact with their family, no phone contact, only once have German diplomats visited these journalists. They are under pressure," she added, stressing that she was not offended.

The television report said the pair were arrested at the office of Mohammadi-Ashtiani's lawyer while trying to interview her son and after taking pictures of Tabriz prison, were the woman is held.

Mohammadi-Ashtiani's case, revealed last summer by human rights associations, has triggered an international outcry.

The Germans, who entered the country on tourist visas, reportedly work for the Springer group in Germany. Foreign reporters need special press visas to be able to work in Iran.

In Berlin, the German foreign ministry told AFP "we are following the news. But for the moment we have no specific information about it."

It also said the pair have had "intensive consular assistance."

Later, the ministry said a German diplomat received access to them on Tuesday.

"A staff member from the German embassy in Tehran had the opportunity for a second consular visit with the two jailed German nationals in Tabriz," a statement said.

"The German government continues to work intensively on the quickest possible resolution of the case."

Iran has also accused three American hikers detained on July 31, 2009 of espionage and illegal entry from across the border with neighbouring Iraq.

Two of the three -- Josh Fattal and Shane Bauer -- have been held in a Tehran jail for more than a year. Their female companion, Sarah Shourd, was released on bail last month.

All three, along with US authorities, have insisted they were not inside Iranian territory.