Britain’s top military officer said Wednesday the country’s fleet of combat jets is stretched to the limit and could struggle to take on additional roles in fighting Islamist extremists in the Middle East without scaling back elsewhere.

Army Gen. Nicholas Houghton told the Royal United Services Institute think tank’s annual air power conference that “those who observe that further national employment of fast jets to meet the proliferating problem of [Islamic State] is a zero-sum game have got it about right….”

Gen. Houghton, Britain’s chief of defense staff, said a vastly smaller Royal Air Force, which is busy with domestic and overseas security roles while also transitioning between generations of combat aircraft, “have put us at the very limits of fast jet availability and capacity.”

He said the situation was one reason the country would extend the use of Tornado combat jets now used heavily in Iraq and would show “unwavering commitment” to the Lockheed Martin Corp. F-35 Joint Strike Fighter the country plans to introduce in coming years.

Image: UK Gen. Sir Nicholas Houghton and US Gen. Martin Dempsey, Jan. 22, 2015 (photo: D. Myles Cullen/Department of Defense)