US President Donald Trump's eldest son and a former campaign manager will testify before Congress next week, a Senate panel announced Wednesday, in what could be a crucial step in the ongoing Trump-Russia investigation.

Donald Trump Jr and Paul Manafort are scheduled to testify before the Senate Judiciary Committee next Wednesday at 10 am (1400 GMT).

Both men attended a controversial meeting with a Russian lawyer last year in which they were expecting to receive dirt from Moscow on Donald Trump's 2016 election rival Hillary Clinton.