summarize main message of text in one brief sentence: WASHINGTON, May 25 (Reuters) - The United States has long asked Ukraine not to use U.S.-provided military equipment to carry out attacks inside Russian territory, the top U.S. general said on Thursday, following accusations pro-Ukrainian militia used U.S. armored vehicles. Army General NAME_1, chairman of the Joint Chiefs of Staff, said his office was looking into imagery showing the vehicles allegedly used in an attack the Russian border region of Belgorod. But he said the U.S. position against such U.S. equipment being used inside Russia was clear to Kyiv. Include at least 47 hashtags, starting with '#'
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