United States president Donald Trump has gone on the record to deny any collusion between him and the Russian government.
Mr Trump is facing the biggest crisis of his presidency.
He allegedly tried to quash an investigation into former national-security adviser Michael Flynn's suspected links to Russia.
And he has also admitted he disclosed security details with Russian foreign minister Sergei Lavrov last week.
Now, former FBI director Robert Mueller has been named as special counsel to oversee an investigation into the claims against President Trump and his campaign team.
After holding talks with the Colombian president at the White House, Mr Trump addressed the appointment at a media conference for the pair.
"Well, I respect the move, but the entire thing has been a witch-hunt. And there is no collusion between, certainly, myself and my campaign, but I can always speak for myself and the Russians, zero. I think it divides the country. I think we have a very divided country because of that and many other things."
President Trump is alleged to have asked then-FBI director James Comey to drop General Flynn's case in February.
Asked by a journalist if it were true, the President was emphatic.
(Reporter:) "Did you, at any time, urge former FBI director James Comey, in any way, shape or form, to close, or to back down, the investigation into Michael Flynn? And, also, as you look back ..."
(Trump:) "No, no. Next question."
Politicians on both sides of Congress have welcomed Robert Mueller's appointment.
Leading opposition Democrat Nancy Pelosi says Donald Trump should allow a fully independent inquiry if he has nothing to hide.
But she says she has concerns Mr Mueller will still be subject to the supervision of the Trump-appointed leadership at the Justice Department.
"A special prosecutor cannot take the place of a truly independent, outside commission that is completely free from the Trump administration's meddling. A commission is also necessary to address the broader vulnerability of our elections to foreign interference in the future. That is one of the reasons we need an outside, independent counsel."
It has also emerged that Michael Flynn and other Trump advisers were in notable contact with Russian officials and others linked to the government during the election campaign.
They engaged in at least 18 calls and emails during the last seven months of the race.
Republican House Speaker Paul Ryan says he wants investigators to be left alone now to do their jobs.
"I believe that the professionals of the Justice Department need to do their jobs independently, objectively and thoroughly, and I believe the special counsel, which is Robert Mueller now, helps them do that."
Mr Ryan says he disagrees with claims a Justice Department investigation could interfere with a congressional investigation.
"No, it doesn't, actually. So, we are going to keep these investigations going here. As I've always said, I think the intelligence committees are the right place to do that. This is an investigation involving Russia, involving another country interfering with our elections, and so the intelligence committee, in my opinion, is the best place for that. And so, these bipartisan, bicameral investigations -- House Intelligence Committee, the Senate Intelligence Committee -- are going to continue their investigations."
Donald Trump fired James Comey in the wake of the investigation into Russia connections.
Leading Democrats have since called for Mr Trump's impeachment.
He dismisses that idea, claiming even his enemies say there was no collusion.
"I think it's totally ridiculous. Everybody thinks so. Director Comey was very unpopular with most people. When I made that decision, I actually thought that it would be a bipartisan decision, because you look at all of the people on the Democratic side, not only the Republican side, that were saying such terrible things about Director Comey."
Mr Trump had already tweeted his claim about the appointment of a special counsel being a witch-hunt before the press conference.
A key Democratic senator, Dick Durbin, says he believes the President's twitter activity will lead to his downfall.
"This has now become standard operating procedure in the Trump White House. The night before, they say something responsible and thoughtful, and then, sometime in the middle of the night or early-morning hours, the President tweets the exact opposite. The President is his own worst enemy. He is going to basically hang himself with 140 characters at a time on a tweet."
Donald Trump is set to leave for his first overseas trips as president now.
He will go first to Saudi Arabia, then Israel and Italy.
