WASHINGTON: Pressure built on the US Congress to pass tough gun control legislation Thursday as the mother of the man arrested for the slaughter of 22 people in El Paso, Texas said she had called police out of concern he had a military-style weapon.

But President Donald Trump and Republicans continued to avoid calls for action against an epidemic of mass shootings, conscious of the importance to the party of gun owners in next year's national elections.

The White House, meanwhile, was accused of using the  two shootings last weekend to promote Trump, after it released a video of a hospital visit to shooting victims. An aide gushed it showed him being greeted like a "rock star."

Lawyers for the mother of Patrick Crusius, the accused El Paso shooter, said she had called police in Allen, Texas weeks before the August 3 attack because she was concerned about his owning an AK-47-type assault rifle.

The lawyers, Chris Ayres and R. Jack Ayres, of Dallas, told CNN that Crusius's mother was worried given her son's age, maturity level and lack of experience with such a weapon.

But a police officer told her that her 21-year-old son was legally able to purchase the weapon, and nothing was done about the "informational" call, according to the lawyers.

- Angry US mayors -

The news fed into the mounting anger in the wake of the back-to-back shootings in El Paso on Saturday and Dayton, Ohio on Sunday, which together left 31 dead and many more injured. Both attacks were carried out by solitary white men armed with assault weapons.

In an open letter, 214 US mayors demanded that the Republican-controlled US Senate be recalled from its summer break to immediately pass gun control legislation already approved in February in the Democrat-lead House of Representatives.

Their letter, addressed to Senate Majority Leader Mitch McConnell and top Democrat Chuck Schumer, noted there have been more than 250 mass shootings in the United States this year.

"The tragic events in El Paso and Dayton this weekend are just the latest reminders that our nation can no longer wait for our federal government to take the actions necessary to prevent people who should not have access to firearms from being able to purchase them," the letter said.

The call added to the pressure on McConnell, who has stifled congressional efforts to expand gun controls amid Republicans' fears that they could suffer at the ballot box in next year's elections.

The letter pointed to two background check bills passed by the House that McConnell has essentially blocked from consideration in the Republican-controlled Senate.

Bryan Barnett, president of the US Conference of Mayors, described his members as being "on the frontlines" of an epidemic of gun violence.

"Keeping our cities safe is not a partisan issue," said Barnett, the mayor of Rochester Hills, Michigan.

The letter came after Trump said on Wednesday that he supported legislation to block gun sales to people with mental health issues, but did not endorse stronger measures.

"I can tell you there is no political appetite for that at this moment," Trump said.

Those measures include universal background checks for all gun sales contained in the House measure, and bans on the assault rifles used in many mass shootings.

- Trump assailed for self-promotion -

Meanwhile Trump was assailed for using his trip to the sites of the two shootings on Wednesday to promote himself.

Trump visited hospitals in both El Paso and Dayton and the White House release photographs and video footage of the visits which showed doctors and nurses applauding him.

"The President was treated like a Rock Star inside the hospital, which was all caught on video. They all loved seeing their great President!" tweeted Dan Scavino, the White House social media director.

"The love, the respect for the office of the presidency, it was -- I wish you could there to see it," Trump told journalists.

Protestors against Trump's visit to El Paso said he was not focusing on the victims and the tragedy.

"In El Paso, we're still healing right now, and right now he's taking all the front from the victims," said Bill Cooks.

"The only thing we're talking about is Trump right now, we're not talking about the victims, and Trump needed to stay in Washington and get some new ... gun laws."

Democrats blasted Trump, accusing him of exploiting the mass shootings "for his personal gain."

"Innocent Americans were slaughtered. And you spin a presidential visit like a vanity project," said New York legislator Hakeem Jeffries.—AFP