WASHINGTON - After his former attorney pleaded guilty to lying in hopes of covering up potential Russian ties, President Donald Trump ended his Thursday lashing out at the special counsel investigation and calling for its demise.

In a pair of tweets after landing in Argentina for the G20 summit, the president called the two-year investigation a "total witch hunt" and accused special counsel Robert Mueller of ignoring crimes committed by the "other side."

"This is an illegal hoax that should be ended immediately," the president said on Twitter late Thursday. "Mueller refuses to look at the real crimes on the other side. Where is the IG REPORT?"

It's far from the first time the president has attacked Mueller and his investigation into Russian meddling in the 2016 election, but as time has gone on, Mueller's investigation has inched closer to the president and his closest advisers.

More:Robert Mueller probe: Ex-Trump lawyer Michael Cohen pleads guilty to lying to Congress

More:Northern California, reeling from Camp Fire devastation, evacuates from flash floods

More:Report: Trump Organization planned to give $50 million penthouse to Putin amid Moscow deal

Earlier Thursday, Michael Cohen, the president's former attorney and fixer, pleaded guilty to lying to Congress in an aim to cover up Trump's ties to Russia, court documents show.

Cohen admitted to lying about plans for a Trump Tower in Moscow, telling lawmakers the plans ended in January 2016 when it really lasted well into Trump's presidential campaign.

Prosecutors said that Cohen lied to the committees to “minimize links between the Moscow Project and (Trump) and give the false impression that the Moscow Project ended before the Iowa caucus and the very first primary in hopes of limiting the ongoing Russia investigations.”

After the guilty plea was made public, Trump fought back on criticism and what the plea deal could mean for him. He called Cohen "a weak person" and said even if his testimony were true, it was perfectly legal for him to negotiate a real-estate deal while campaigning.

“He's a weak person and not a very smart person," Trump said. "Even if he was right, it doesn't matter because I was allowed to do whatever I wanted during the campaign. I was running my business."

The guilty plea came amid a flurry of activity from Mueller, who personally signed Cohen's deal. On Monday, Mueller voided a plea deal with Paul Manafort, Trump's former campaign chairman, for lying repeatedly to investigators. Manafort has a hearing Friday to get a possible sentencing date for charges of conspiracy and obstruction of justice for representing a pro-Russia faction in Ukraine.

Contributing: Kevin Johnson