A pigeon flies in front of the Kremlin's Spasskaya tower (L) and Saint Basil's cathedral (C) in Moscow on March 1, 2023.

Initial U.S. intelligence suggesting that China is considering supplying lethal aid to Russia for its war in Ukraine was gleaned from Russian government officials, according to one current and one former U.S. official familiar with the intelligence.

U.S. officials then spent weeks corroborating the information from other sources of intelligence, the current and former officials said, and with allies who also brought additional streams of information.