By Kanishka Singh WASHINGTON (Reuters) – The U.S. Treasury Department should do more to ensure that major tech firms, including Meta Platforms and Alphabet, comply with sanctions against foreign firms that advertise on their platforms, a top lawmaker said on Monday. Democratic U.S. Senator Mark Warner, who heads the Senate Intelligence Committee, wrote a letter to Treasury Secretary Janet Yellen in which he said the Treasury Department was failing to “ensure sanctions compliance in digital advertising markets.” American technology firms like Alphabet, which owns Google, and Meta, which owns Fa…