A top Swedish diplomat has been found dead after being arrested on suspicion of espionage.

Sweden's SAPO security service had detained the man on Sunday and kept him for questioning until Wednesday, when he was released, although he remained subject to investigation, the country's prosecution service said.

The crimes were reportedly committed between May 1 and May 11 this month.

They would not, however, confirm whether the diplomat who died was the same man they arrested.

'We have seen this information that the Ministry of Foreign Affairs has stated that an employee has died,' SAPO spokesperson Johan Wikström said.