Paris

Global politics has soured the run-up to this week's TNT2006 Trends in Nanotechnology conference in France. Organizers initially banned some 15 Iranian researchers from attending, citing political concerns over Iran's nuclear programme.

The decision has since been revoked and two Iranians will now attend the conference on 4–8 September in Grenoble. The remainder have withdrawn, according to the organizers, because of problems such as visa delays. But the incident has raised concerns that the current political situation, in which Iran faces international isolation over its refusal to stop its uranium enrichment programme, may cause scientists from the country to be ostracized.

Those involved in the conference have denied any discrimination against Iranian scientists, and say the incident is the result of a series of misunderstandings about the security-clearance rules. The congress centre in which the conference is being held is inside Minatec, a sprawling research and industrial complex that belongs to the French Atomic Energy Commission (CEA).

When Antonio Correia, president of conference organizers the PHANTOMS Foundation in Madrid, began receiving submissions from Iran he contacted Didier Molko, CEA director of Minatec, to check whether this raised any security concerns. Molko told him that “CEA rules say that Iranian people can't go in”. As a result, Correia e-mailed the Iranian applicants on 9 June, apologizing that “we must withdraw your contribution and participation”, a move he says met an angry response. “I understand that people were angry,“ says Correia. “Science should have nothing to do with politics.”

Molko now says his initial decision was a personal mistake, and not CEA policy. He was being cautious because of the political situation, he says, but after checking with his superiors in Paris, he revoked his earlier decision. “It was a delay of a week or two at most.”

Pascal Newton, a spokesman for CEA headquarters in Paris, says that the commission's security services check out all visitors to CEA buildings on a case-by-case basis. “We get a simple, yes/no; we never know why.” Particular nationalities aren't officially banned, he says, although he adds: “In the current political context, I can imagine Iran might be more sensitive.”

In the long term, the best scientists will continue to collaborate with Iranian scientists.

The United Nations Security Council set a deadline of last week for Iran to suspend uranium enrichment activities, which it suspects are part of a programme to develop nuclear weapons. Iran ignored the deadline and, failing last-ditch negotiations this week, the council is set to impose economic sanctions on the country.

International isolation in similar situations has in the past spared scientific cooperation. Indeed, during the cold war, contact between scientists was one of the few channels open between East and West. But Reza Mansouri, a well-known Iranian physicist based at the Sharif University of Technology in Tehran, complains that his country's scientists are already falling victim to discrimination, such as visa delays. He also worries about what he sees as widespread ostracization by fellow scientists, and he deplores the incident in France.

But Mansouri says he believes it is a temporary problem induced by the tense international climate. “In the long term, the best scientists will continue to collaborate with our scientists, bringing more rationality and understanding into the dialogue, and ultimately more peaceful attitudes.”