Video report by ITV News Security Editor Rohit Kachroo
A shooting at a department store in El Paso, Texas on Saturday left 22 people dead and nine people were killed when a gunman opened fire on revellers in Dayton, Ohio in the early hours of Sunday morning.
Dozens of people were left injured in the two attacks, which became the 250th and 251st mass shootings in the US this year.
Mr Trump was speaking at a press conference on Monday where he vowed "to act with urgent resolve."
Speaking from the White House: "In one voice, our nation must condemn racism, bigotry and white supremacy, these sinister ideologies must be defeated.
"Hate has no place in America, hatred warps the mind, ravages the heart and devours the soul."
The president described the weekend shootings in Texas and Ohio as "barbaric" attacks and crimes "against all humanity" and called for bipartisan cooperation to strengthen the nation's gun laws but offered no details.
He also misstated the location of one of two mass shootings during his speech condemning the violence, referring to Toledo, Ohio instead of Dayton, Ohio.
"May God bless the memory of those who perished in Toledo, may God protect them."
He faces staunch criticism from Democrats, who said he should bear some responsibility for the shootings and his 'hate rhetoric' which they say helps to fuel division.
Could this be a turning point for gun control in the US? ITV News Security Editor Rohit Kachroo reports from El Paso.
Senator Kamala Harris of California found blame in Mr Trump’s use of language, which she said has “incredible consequence”.
“We have a president of the United States who has chosen to use his words in a way that have been about selling hate and division among us,” she told reporters before attending services at a black church in Las Vegas.
As politicians point fingers at Mr Trump, the president said the attacks illustrate the mental illness problem in the US, saying "mental illness and hatred pulls the trigger, not the gun," indicating he would oppose large-scale gun control efforts pushed by Democrats
He also said the internet and video games play a part in the "glorification of violence" in society and called for law enforcement and social media companies to do more to combat extremism and spot warning signs of violence online.
Mr Trump said: "It is too easy today for troubled youths, to surround themselves with a culture that celebrates, violence, we must stop or substantially reduce this and it has to begin immediately."
He called for "red flag laws" to separate individuals believed to have a mental illness from firearms.
Mourners urge politicians to 'do something' in wake of Dayton shooting
Hundreds of people gathered to honour the nine victims killed and 27 injured after a masked gunman opened fire on people enjoying the summer nightlife in Dayton, Ohio.
The crowds, released doves, and repeated the names of the dead, but directed an angrier chorus at Republican governor Mike DeWine, interrupting his speech at the vigil with chants of “make a change” and “do something!”
Mayor Nan Whaley implored the crowd to honour the victims of the second US mass shooting in less than 24 hours.
Connor Betts, 24, was armed with a .223-calibre rifle with magazines capable of holding at least 100 rounds of ammunition when he fired off dozens of shots in a popular entertainment district, Police Chief Richard Biehl said.
Betts was gunned down within 30 seconds of the start of his rampage, police said.
His 22-year-old sister, Megan Betts, was the youngest of the victims.
Police identified the others as Monica Brickhouse, 39; Nicholas Cumer, 25; Derrick Fudge, 57; Thomas McNichols, 25; Lois Oglesby, 27; Saeed Saleh, 38; Logan Turner, 30; and Beatrice N Warren-Curtis, 36.
The gunman was white and six of the nine killed were black, police said.CCTV video they shared shows officers shot Betts at the doorstep of further destruction, just stopping him from entering a bar where some people took cover when the chaos broke out at around 1am on Sunday in the historic Oregon District.
Had he gone inside Ned Peppers Bar, the result would have been “catastrophic”, Mr Biehl said.
Although they will investigate the possibility of a hate crime, they said the quickness of the rampage made any discrimination in the shooting seem unlikely.
Officials said 27 more people were treated for gunshots or other injuries suffered while fleeing, and at least 15 of those have been released. Several more were in serious or critical condition, hospital officials said.
Nikita Papillon, 23, was across the street at Newcom’s Tavern when the shooting started.
She said she saw a girl she had talked to earlier lying outside Ned Peppers, a bar she described as the kind of place “where you don’t have to worry about someone shooting up the place”.
“People my age, we don’t think something like this is going to happen,” she said. “And when it happens, words can’t describe it.”
The Ohio shooting came hours after a man opened fire in a crowded El Paso, Texas, shopping area, leaving 20 dead and more than two dozen injured.
Texas gunman could face death penalty
The shooting that killed 20 people at a crowded El Paso department store in Texas will be handled as a domestic terrorism case, authorities have said said.
Using a rifle, the El Paso gunman opened fire on shoppers during the busy back-to-school season on Saturday afternoon.
The attack targeted a Walmart and did not spread to other nearby shopping areas, El Paso police sergeant Robert Gomez said.
Police weighed hate crime charges against the suspected gunman that could carry the death penalty.
A local prosecutor announced that he would file capital murder charges, declaring that the alleged assailant had “lost the right to be among us”.
Investigators focused on whether the El Paso attack was a hate crime after the emergence of a racist, anti-immigrant screed that was posted online shortly beforehand.
Detectives sought to determine if it was written by the man who was arrested.
It comes as far-right internet forum 8chan, which has been linked to mass shootings in the US, loses its cybersecurity protection after its provider cut off support.
Cloudflare said it had terminated the website as a customer and called the forum a “cesspool of hate”.
Matthew Prince, Chief Executive of Cloudflare, claimed the suspect in the El Paso attack had posted to 8chan before commencing the attack.
Law enforcement officials identified the suspect as 21-year-old Patrick Crusius from Allen, a Dallas suburb which is a nearly 10-hour drive from El Paso.
The border city of El Paso has figured prominently in the immigration debate and is home to 680,000 people, most of them Latino.
Crusius surrendered after being confronted by officers on a pavement close to the scene. Police did not know how many bullets were fired or why the attack stopped, Mr Gomez said.
“We don’t have information on what prompted him to stop firing,” he added.El Paso Police Chief Greg Allen said the suspect was cooperative and “forthcoming with information”.
Relatives said a 25-year-old woman who was shot while apparently trying to shield her two-month-old son was among those killed. Mexican officials said six Mexican nationals were also among the dead.
Authorities searched for any links between the suspect and the material in the document that was posted online, including the writer’s expression of concern that an influx of Hispanics into the United States will replace ageing white voters, potentially turning Texas blue in elections and swinging the White House to Democrats.
The writer was also critical of Republicans for what he described as close ties to corporations and degradation of the environment.