YEHUD, Israel (AP) — Israel, one of the pioneers of drone warfare, is now on the front lines of an arms race to protect against attacks by the unmanned aircraft.

A host of Israeli companies have developed defense systems they say can detect or destroy incoming drones. But obstacles remain, particularly when operating in crowded urban airspaces.

Ulrike Franke, a policy fellow at the European Council of Foreign Relations, said: "Fighting these systems is really hard ... not just because you need to detect them, but you also need to detect them everywhere and all the time."

A series of drone strikes across the Middle East, including an attack on a Saudi oil field and processing plant that jolted international markets earlier this month, have underscored the devastating effectiveness of small unmanned attack aircraft.