This is true.
On 16 March 2019, Agence France Presse published an article relating to the NZ Mass Shooting incident of 15 March 2019. A copy is accessible in the link below.
The article stated amongst other things that:
“US President Donald Trump condemned the “horrible massacre” in which “innocent people have so senselessly died”, but denied that the problem of right-wing extremism was widespread.”
The above statement appears to have been made based on a Twitter post from the US President’s Twitter account.
My warmest sympathy and best wishes goes out to the people of New Zealand after the horrible massacre in the Mosques. 49 innocent people have so senselessly died, with so many more seriously injured. The U.S. stands by New Zealand for anything we can do. God bless all!
— Donald J. Trump (@realDonaldTrump) March 15, 2019
The denial given by President Trump, however, was reported in a media interview with the President in the Oval Office. He is reported to have said:
“I think it’s a small group of people that have very, very serious problems, I guess. If you look what happened in New Zealand, perhaps that’s the case. I don’t know enough about it yet…But it’s certainly a terrible thing.”