Iran has detained 20 individuals it claims are operatives of Israel's Mossad spy agency, according to the country's judiciary. The announcement comes days after the execution of a nuclear scientist convicted of passing sensitive information to Israel. While some of those arrested have reportedly been released after charges were dropped, officials have warned that no leniency will be shown to those found guilty. Executions for espionage have risen sharply in Iran this year, with at least eight carried out in recent months. The arrests and executions follow a period of heightened tensions, including Israeli air strikes on Iranian targets and retaliatory missile and drone attacks.