Israel and the United States are battling over the sale of the next generation of warplanes, the F-35, with Israel considering canceling plans to purchase some 100 aircraft, IDF officials said Monday. Israel is insisting it be allowed to upgrade the planes with its own technological warfare systems, as it has done with the F-15, the F-16 and the F-16-I, the officials said, speaking on condition of anonymity because the sides are trying to resolve the issue. The United States has rejected Israel's request, at least partly because the Israeli systems are considered the best in the world and provide stiff competition to US companies, the officials said. Israel was reinstated as a partner in the development of the F-35, also known as the Joint Strike Fighter (JSF), after Israeli participation was put on hold following the Chinese arms deal crisis. Israeli participation in JSF development was suspended as part of US sanctions against Israel following the Israeli agreement to upgrade Chinese 'Harpy' UAV's, which was done without prior consultation with the US. Israeli defense industries expect to sign contracts worth tens of millions of dollars as part of the project. The JSF, also known as the F-35 fighter, is supposed to serve as the major aviation platform for all branches of US military and for many military forces around the world, replacing the F-15 and F-16 fighters.