President Donald Trump thinks that Russia interfered in the 2016 U.S. election but also believes other countries may have meddled, too.

"Well I think it was Russia and I think it could have been other people and other countries. It could have been a lot of people that interfered," Trump said Thursday at a press conference in Warsaw, Poland.

"It could have very well been Russia but it could well have been other countries and I won't be specific but I think a lot of people interfered," Trump also said. "Nobody really knows. Nobody really knows for sure."

"The thing I have to mention is that Barack Obama when he was president found out about this in terms of if it were Russia, found out about it in August, now the election was in November, that's a lot of time he did nothing about it. Why did he do nothing about it? He was told it was Russia by the CIA as I understand it. ... I think what happened was that he thought that Hillary Clinton was going to win the election and he said let's not do anything about it. "

Trump said only three or four intelligence agencies found that Russia had interfered in the election, not the previously reported 17. His comments were made hours before his first face-to-face encounter with Russian President Vladimir Putin.