BEIJING, June 19 (Reuters) - U.S. Secretary of State Antony Blinken said on Monday he had asked China's government to be vigilant about private companies that may be providing Russia with technology that could be used against Ukraine, although he said he had seen no evidence Beijing is providing lethal assistance to Moscow. "What we do have ongoing concerns about, though, are Chinese firms, companies, that may be providing technology that Russia can use to advance its aggression in Ukraine and we have asked the Chinese government to be very vigilant about that," Blinken told reporters. Blinken spoke on a...