They wrote to the Senate's Republican Majority Leader Mitch McConnell and top Democrat Chuck Schumer demanding the chamber approve bills passed by the lower House requiring background checks for all gun purchases and regulation of secondary sales.

"Already in 2019, there have been over 250 mass shootings," said the 214 members of the influential US Conference of Mayors, including Dee Margo of El Paso, Texas and Nan Whaley of Dayton, Ohio -- the two cities where 31 people were gunned down at the weekend.

The call will add to the mounting 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 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 conference's president, Bryan Barnett, described his members as being "on the frontlines" of an epidemic that cannot wait for a federal government solution.

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

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

If one of the two bills had been law in 2015, the mayors' letter said, "the terrible tragedy that occurred at the Emanuel AME Church in Charleston might have been avoided."

On June 17, 2015 white supremacist Dylann Roof murdered nine African-Americans in a church in Charleston, South Carolina.

Despite a criminal background Roof was able to buy the handgun he used in the shooting.

On Wednesday President Donald Trump said he supported proposed legislation in the Senate that would block gun sales to people with mental health issues.

But Trump said he did not think there was political support for tougher legislation, like that passed already by the House, or bans on highly lethal assault rifles used in many mass shootings.