Iran said on Saturday it had arrested a Swedish national on allegations of espionage, while Sweden’s foreign ministry said the case related to an arrest previously revealed in May.

The announcement comes amid diplomatic tensions between Tehran and Stockholm, after a Swedish court sentenced a former Iranian prison official to life for war crimes during mass executions in the Islamic republic in 1988.

Iran’s intelligence ministry said it had “identified and arrested a national of the Kingdom of Sweden suspected of espionage”, without providing details on the suspect’s identity nor the date of their detention.

“In all the previous trips, the suspect… communicated with a number of European and non-European suspects who were under surveillance in Iran,” the Iranian statement read.

In early May, the Swedish foreign ministry said a Swede in his 30s had been arrested in Iran.

The ministry confirmed that Saturday’s announcement referred to the same case, adding: “This is a previously known case that the foreign ministry is already working on.”

The Iranian statement said that “the suspect in question re-entered the country a few months ago after the arrest of another European spy” to collect information, adding the suspect had been taken into custody while leaving Iran.

The intelligence ministry said the suspect had visited Israel, the Islamic republic’s arch-enemy, before going to Iran.

It also alleged Sweden had “supported several proxy spies” for Israel, including Ahmadreza Djalali, a Swedish-Iranian academic who has been sentenced to death in the Islamic republic.

Djalali’s sentence was issued in 2017 after he was convicted of passing information about two Iranian nuclear scientists to Israel’s Mossad spy agency that led to their assassinations. He was granted Swedish citizenship the following year.

His case was followed by the trial in Stockholm of Hamid Noury, a former official in Iran’s judiciary accused of war crimes over the killing of prisoners in Iran during the 1980s.

Noury received a life sentence from a Swedish court on July 14. Iran dismissed the verdict as “political” and has called for his release.

Relations between to the two countries have been strained over the case, with Tehran recalling its ambassador to Sweden for consultations a week later.