President Donald Trump on Thursday accused his former personal lawyer Michael Cohen of "lying" to federal prosecutors about a proposed real estate project in Russia in order to get a reduced sentence for a new guilty plea and for a prior one.

Trump spoke to reporters on the South Lawn of the White House about an hour after Cohen entered a new guilty plea in federal court in Manhattan to lying to Congress about details of that Trump Tower project in Moscow.

Cohen admitted in that plea to misleading a committee about the extent of Trump's involvement in and knowledge of that project, which never came to fruition.

"He's a weak person and not a very smart person," Trump said of Cohen, who had served as his lawyer and fixer for years.

"Michael Cohen is lying," Trump said. "He's lying, very simply to get a reduced sentence."

A reporter asked the president: "If Cohen is such a bum, why did you hire him, have him on your payroll for 12 years and have him do so much of your dirty work?"

Trump replied: "Because a long time ago he did me a favor. A long time ago he did me a favor."

The president did not elaborate on the nature of that favor.

Cohen as part of his plea signed a cooperation agreement with special counsel Robert Mueller, who is investigating Russian interference in the 2016 presidential election, possible collusion by the Trump campaign, and possible obstruction of justice by the president.