The US National Academies are advising American scientists to avoid travelling to Iran, following the detention in December of one of the academies' top officials.

Glenn Schweitzer, a veteran physicist who manages scientific visits and exchanges in Eurasia for the National Academy of Sciences, was in Iran as part of a long-running programme between the academy and Iranian scientific organizations. The programme promotes collaboration and aims to keep scientific diplomatic channels open between the two countries despite the continuing political confrontation.

Schweitzer was detained on two occasions by three men claiming to be from the Iranian security services, who threatened to prevent him from leaving the country if he did not cooperate, he says. The academies say that visits will resume only if the Iranian government provides firm assurances that US scientists can visit the country safely.