Thursday’s attack followed one by Iran inside Pakistan on Tuesday. The strikes imperiled diplomatic relations between Islamabad and Tehran, as Iran and nuclear-armed Pakistan have long regarded each other with suspicion over militant attacks. Iran has seen growing pressure for action after the Islamic State group attack, Israel’s war on Hamas and wider unrest against its theocracy. Iran and Pakistan share a 900-kilometer (560-mile), largely lawless border in which smugglers and militants freely cross. For both Iran and Pakistan, the cross-border attacks renew questions about their own military preparedness, particularly their radar and air defense systems.