A former Iranian ambassador to Argentina, wanted there in connection with the 1994 bombing of a Jewish cultural centre, has been arrested in the UK.
No one has been charged over the 1994 bombing
The former ambassador, Hadi Soleimanpour, is due to appear in court in London on Friday.
Magistrates will decide whether to extradite him to Argentina to face charges of conspiracy arising from the attack, in which 85 people were killed.
The Argentine intelligence service has long believed Iran was behind the car bomb attack in Buenos Aires - a charge Iran has repeatedly denied.
Mr Soleimanpour, 47, was arrested in northern England, where he works as a research assistant at Durham University.
"This is extremely important because it is the first arrest in the international leads in this case, and starting from it we can make progress on how the attack was organised," Marta Nercellas, a lawyer for the Argentine Jewish Associations Federation, told reporters.
The extradition warrant was one of eight issued by an Argentine judge, Juan Jose Galeano, against Iranian citizens last week.
Similar warrants issued in March against four Iranian diplomats caused tension between Buenos Aires and Tehran, and resulted in the recall of the Iranian ambassador.
The community centre that was blown up was the main such centre for Jews in Argentina, which has the largest Jewish population in Latin America.
Last month, Argentine President Nestor Kirchner said the lack of progress in the case was a "national disgrace" and vowed to bring those responsible to justice.