A lawyer for U.S. President Donald Trump on Sunday sharpened his attacks on the special counsel inquiry into possible Trump campaign collusion with Russia, calling it "the most corrupt investigation that I've ever seen."

That charge by lawyer Rudy Giuliani came a day after Trump himself launched a fresh attack on the investigation, assailing it in successive Twitter messages as a "Rigged Witch Hunt" and a "Democrat Con Job!"

The investigation, headed by former FBI director Robert Mueller, has widely been expected to wind up in the next few months — possibly after a Mueller interview with Trump — but Giuliani said such a meeting now seemed increasingly unlikely.