Britain has rejected Argentina's request for the extradition of a former Iranian diplomat accused in the bombing of a Jewish centre.
Mr Soleimanpour (right) denies any involvement in the bombing
The Home Office said there was not enough prima facie evidence for the extradition of Hade Soleimanpour to proceed at this stage.
The case has strained ties between Britain and Iran, which said it was politically motivated.
The 1994 attack on the Buenos Aires Jewish centre killed 85 people.
Mr Soleimanpour, 47, was arrested in Britain in the northern city of Durham while studying at university.
He was later released on £730,000 ($1.2m) bail partly paid by the Iranian authorities.
A former Iranian ambassador to Argentina, he has denied the charges, saying he was outside the country at the time of the bomb.
No-one has been charged over the bombing
"There is really no evidence at all implicating Soleimanpour in
the very serious crimes alleged," his lawyer Ben Brandon told AFP
However, in a 2,600-page dossier the Argentines say Mr Soleimanpour provided support to the bombers who were based at the Iranian embassy in Buenos Aires.
Argentina was given four weeks - which was extended by two weeks - to provide the evidence for the case which has considerably strained Britain's relations with Tehran.
Iran has recalled its ambassador to London after the former diplomat's arrest and has also cut economic and cultural ties with Argentina.
There are around 300,000 Jews in Argentina - which is the largest Jewish population in Latin America.
"We deplore the decision that has just been taken in Great Britain," said Alfredo Neuburger, a spokesman for a group of Argentine Jewish organisations, the Daia.
"We are convinced that existing evidence warrants the interrogation of the former Iranian ambassador
by the Argentine judicial system."
Britain has said that the case could be resumed if Buenos Aires provides sufficient evidence.