WASHINGTON (Reuters) - A Republican-controlled U.S. House of Representatives committee asked President Joe Biden's son Hunter Biden to testify in an open hearing on March 20, as it continues its impeachment probe of his father, the panel said in a Wednesday statement.

The House Oversight Committee has focused on Hunter Biden's work for businesses based in countries such as Ukraine and China while his father served as U.S. vice president from 2009 to 2017. So far they have turned up no evidence of wrongdoing by the elder Biden, even as they have highlighted his son's struggles with substance abuse.

The panel also invited three of Hunter Biden's former business associates.

Hunter Biden, who has worked as an investor and lawyer and sold his own paintings, testified in a closed-door interview last month as part of the inquiry. He had initially said he would only testify publicly, but reversed course after lawmakers threatened to hold him in contempt.

In the hours-long interview that turned at times contentious, he said repeatedly in that his father had no involvement with and drew no benefit from his business activities.

A representative for Hunter Biden did not immediately respond to a request about whether he would attend the hearing.

(Reporting by Jasper Ward and Makini Brice; Editing by Eric Beech and Scott Malone)