United States intelligence agencies were caught by surprise when fighters from the Islamic State of Iraq and al-Sham (ISIS) seized two major Iraqi cities this week and sent Iraqi defense forces fleeing, current and former U.S. officials said Thursday. With U.S. troops long gone from the country, Washington didn’t have the spies on the ground or the surveillance gear in the skies necessary to predict when and where the jihadist group would strike.

The speed and ease with which well-armed and highly trained ISIS fighters took over Mosul, Iraq’s second-largest city, and Tikrit, the birthplace of former Iraqi ruler Saddam Hussein, have raised significant doubts about the ability of American intelligence agencies to know when ISIS might strike next, a troubling sign as the Islamist group advances steadily closer to Baghdad. And it harkened back to another recent intelligence miscue, in February, when U.S. spy agencies failed to predict the Russian invasion of Crimea. Both events are likely to raise questions about whether the tens of billions of dollars spent every year on monitoring the world’s hot spots is paying off — and what else the spies might be missing.