Trump, accused by Democrats as stoking racial divisions, said Americans must "condemn racism, bigotry and white supremacy," a day after Texas officials said racial hatred was a possible motive in the killings of 22 people in the southern border town of El Paso.
A 21-year-old white man has been charged with capital murder in Saturday's shooting spree. Police in El Paso cited a racist, anti-immigrant manifesto posted online shortly before the shooting, which they attributed to the suspect, Patrick Crusius.
Trump did not address accusations that his own anti-immigrant and racially charged comments have contributed to a rise in race tensions, nor did he call for broad gun control measures.
"These sinister ideologies must be defeated," he said in remarks at the White House. "Hate has no place in America. Hatred warps the mind, ravages the heart and devours the soul."
Democrats, who have long pushed for stricter gun control, quickly accused Trump of hiding behind talk of mental health reform and the role of social media instead of committing to laws aimed at curbing gun violence in the United States.
They blamed Trump indirectly for the attack in Texas, citing his rhetoric on immigrants.
Former President Barack Obama, who fought unsuccessfully for gun restrictions while in office, did not mention Trump by name on Monday when he urged Americans to reject divisive rhetoric.
"We should soundly reject language coming out of the mouths of any of our leaders that feeds a climate of fear and hatred or normalizes racist sentiments," Obama said in a statement. "It has no place in our politics and our public life."
Janet Murguia, the President of UnidosUS, the biggest Hispanic advocacy group in the United States, called Trump the "radicalizer-in-chief" at the group’s annual conference in San Diego, shortly before five Democratic presidential candidates, including front-runner Joe Biden, were due to speak there.
Trump began his presidential campaign in 2015 by characterizing Mexican immigrants as rapists and drug smugglers and he has repeatedly likened immigrants crossing the border from Mexico as an "invasion." He also has called them "very bad thugs and gang members."
On Saturday, several Mexican citizens were among the 21 people killed at a Walmart by a man who drove from his home in Allen, Texas, 660 miles (1,062 km) away, to El Paso, authorities said.
Just 13 hours later, another gunman killed nine people in downtown Dayton, Ohio. The suspect, Connor Betts, was killed by police in less than a minute. His motive was not clear.
RED FLAGS AND BACKGROUND CHECKS?
Mass shootings by lone attackers in recent years have increased concerns about gun violence and the threat posed by racist and white supremacist ideologies.
Trump, who has been accused of not doing enough to tackle domestic extremist groups, said he would direct the Department of Justice to investigate domestic terrorism and would propose legislation to ensure that those who commit hate crimes and mass murders face the death penalty.
He also said the country needs to reform mental health laws to identify disturbed people as well as work with social media companies to detect possible mass shooters.
"We must make sure those judged to pose a grave risk to public safety do not have access to firearms and that if they do those firearms can be taken through rapid due process," he said, an apparent reference to "red flag" laws.
Republican US Senator Lindsey Graham, a Trump ally, said he has spoken with Trump about legislation he plans to introduce in September with Democratic Senator Richard Blumenthal. It would direct federal grant money to states seeking to adopt such laws.
The "red flag" bills make it easier for police to confiscate weapons from someone found to pose a threat of violent behavior and have been adopted by some 15 states since a February 2018 shooting at a Parkland, Florida, high school killed 17 people.
Trump earlier on Monday had called for "strong background checks" on gun buyers, but he did not elaborate on the idea and it was not the central part of his White House statement.
"Mental illness and hatred pulls the trigger, not the gun," he said in the address.
That comment drew immediate criticism, with 2020 Democratic presidential candidate Amy Klobuchar accusing Trump of trying to dodge the issue of gun control.
"There's mental illness&hate throughout world, but U.S. stands alone w/high rate of gun violence," she said on Twitter.
The National Rifle Association (NRA), an influential gun rights group, said it welcomed Trump's call to address "root causes" of gun violence, saying those who have been deemed a danger to themselves or others should not have access to firearms.
After a gunman killed 58 people at a country music festival in Las Vegas in 2017, Trump proposed a ban on an attachment known as a bump stock that gives a semi-automatic weapon the capability of a machine gun. The ban went into effect in March.
But Trump stepped back from sweeping changes to gun laws that he had considered after the Parkland shooting. He instead backed more modest measures following a private meeting with the NRA.
POLITICAL DIVIDE
In a morning Twitter post, Trump called on Republicans and Democrats to work together on strong background checks and possibly combine that legislation with "desperately needed immigration reform."
But Democratic lawmakers, who have fought Trump's moves to toughen immigration laws and build a wall along the US-Mexico border, rejected any effort to tie gun control to immigration.
It was not clear what action Trump wants to take with Congress on summer recess and lawmakers not scheduled to return to Washington until September.
The US House of Representatives already has passed a bill calling for universal background checks for gun buyers, but it has not been taken up by the Republican-led Senate.
Democratic Senator Joe Manchin and Republican Senator Pat Toomey said they had spoken to Trump about their bill that would expand background checks to most gun sales and he "showed a willingness to work with us on the issue."