"We have to get it stopped. This has been going on for years... and years in our country," Trump told reporters after the latest US mass shootings in the cities of El Paso, Texas and Dayton, Ohio.

Trump's critics have cited the violence as proof that the president's xenophobic rhetoric toward immigrants and prominent black lawmakers is poisoning the atmosphere in a deeply divided country that has seen a growing number of shootings in recent years.

But speaking to reporters as he returned from a weekend away in New Jersey, Trump said: "Hate has no place in our country and we're going to take care of it."

Trump, who indicated he would make a presidential address on Monday, said he had spoken to Attorney General Bill Barr at length after the shootings and FBI director Christopher Wray, who has been among those warning of the increased threat from white supremacists.

The gunman in El Paso purportedly wrote a manifesto in which he railed against the Hispanic "invasion" of Texas as well as praising the deadly attack on a mosque in New Zealand earlier this year.

Rather than be drawn on the killers' motivations, Trump said they appeared to be suffering from mental illness.

"We're talking to a lot of people and a lot of things are in the works and a lot of good things. And we've done much more than most administrations and it is just not really talked about very much, but we've done actually a lot," he said.

"But this is also a mental illness problem if you look at both of those cases. This is mental illness. These are really people that are very, very seriously mentally ill."