KIEV, Ukraine — The Ukrainian government said on Saturday that it had proof that Russia had provided the surface-to-air missile system that shot down a Malaysia Airlines passenger jet over eastern Ukraine on Thursday, killing all 298 people aboard.

That claim came as officials from Malaysia and the Netherlands pleaded for politics to be put aside so they could recover their dead, still lying in a field in a war zone.

Ukraine also accused Russia and separatist rebels in the east of trying to cover up their role by blocking recovery workers from the crash site, removing evidence and driving three missile launchers back to Russia just hours after the crash.

At a news conference in Kiev, Vitaly Nayda, the head of counterintelligence for the Ukrainian State Security Service, displayed photographs that he said showed the three Buk-M1 missile systems on the road to the Russian border. Two of the devices, missile launchers mounted on armored vehicles, crossed the border into Russia about 2 a.m. Friday, or less than 10 hours after the jet, Flight 17, was blown apart in midair, he said. The third weapon crossed about 4 a.m.