From a publicity standpoint, the attacks in Britain and Iran are a lift to the Islamic State as it loses ground steadily in Syria, Iraq and Libya. Some analysts have interpreted the strikes as a bid by the group to demonstrate its resilience, even as its territory-holding caliphate slowly disappears.

But a review of court records and statements by officials suggests that the violence in London and Tehran was more than just a message. It reflected persistent efforts by the Islamic State since its rise in 2014 to hit targets once thought unassailable — especially in Britain. During this period, officials there intercepted and foiled more than a dozen plots, including five in the past three months.

The number of disrupted plots appears to be far greater in Iran, a Shiite-majority country loathed by the militant Sunni extremists of the Islamic State, which has aimed to hit Iran since at least 2007. A day after the deadly assault last week on the Parliament building and the tomb of Iran’s revolutionary founder, Iranian intelligence officials said they had thwarted 100 terrorist plots in the past two years.