The Times of Israel:
Israel and the United States sent a secret military delegation to Ukraine to test the Russian-made S-300 missile defense system, which Moscow recently provided to Syria, Hadashot TV news reported Monday, citing Syrian and Russian news outlets.
There was no comment on the reports from either Israel or the US. According to the reports, members of the Ukrainian military instructed their US and Israeli counterparts on the capabilities of the system, as well as running through various possible scenarios.
One Russian report said that F-15 planes are training in Ukraine against the S-300 as part of an international exercise that includes Israeli pilots. It wasn’t immediately clear if the Israeli pilots were flying or merely observing from the ground.