WASHINGTON (REUTERS) - Thousands of demonstrators descended on Washington and across the United States on Saturday (June 11), calling on lawmakers to pass legislation aimed at curbing gun violence following last month's massacre at a Texas elementary school.

March For Our Lives (MFOL), the gun safety group founded by student survivors of the 2018 massacre at a Parkland, Florida, high school, said it has planned more than 450 rallies for Saturday, including in New York, Los Angeles and Chicago.

In Washington, 40,000 people assembled at the National Mall near the Washington Monument under light rain, organisers said.

The organisation's 2018 march on Washington, weeks after 17 people were killed at Marjory Stoneman Douglas High School in Parkland, brought hundreds of thousands of people to the nation's capital to pressure Congress to take legislative action, though Republican opposition has prevented any new limits on guns from passing the US Senate.

US President Joe Biden, a Democrat who earlier this month urged Congress to ban assault weapons, expand background checks and implement other gun control measures, said he supported Saturday's protests.

Courtney Haggerty, a 41-year-old research librarian from Lawrenceville, New Jersey, travelled to Washington for the rally with her 10-year-old daughter, Cate, and seven-year-old son, Graeme, to demand congressional action.

Haggerty said the December 2012 school shooting at Sandy Hook Elementary School in Newtown, Connecticut, in which a gunman killed 26 people, mostly six- and seven-year-olds, came one day after her daughter's first birthday.

"It left me raw," she said. "I can't believe she's going to be 11 and we're still doing this." Cate, who is in the fourth grade, said she wanted to attend.

"This is not what I would want my kids to have to be living with," she said.

Pressure on politicians

This year's event in Washington has a simple message to political leaders, according to organisers: Your inaction is killing Americans.

"We are being murdered," said X Gonzalez, a Parkland survivor and co-founder of MFOL, in an emotional speech in which they appeared with survivors of other mass shootings. "You, Congress, have done nothing to prevent it."

A gunman in Uvalde, Texas, killed 19 children and two teachers on May 24, 10 days after another gunman murdered 10 Black people in a Buffalo, New York, grocery store in a racist attack.

The latest mass shootings have added new urgency to the country's ongoing debate over gun violence, though the prospects for federal legislation remain uncertain.

Among other policies, MFOL has called for an assault weapons ban, universal background checks for those trying to purchase guns and a national licensing system, which would register gun owners.

In recent weeks, a bipartisan group of Senate negotiators have vowed to hammer out a deal, though they have yet to reach an agreement. Their effort is focused on relatively modest changes, such as incentivising states to pass "red flag" laws that allow authorities to keep guns from individuals deemed a danger to others.

Speaking to journalists in Los Angeles, Biden said he had spoken several times with Senator Chris Murphy, who is leading the Senate talks, and that negotiators remained "mildly optimistic."

The Democratic-controlled US House of Representatives on Wednesday passed a sweeping set of gun safety measures, but the legislation has no chance of advancing in the Senate, where Republicans have opposed gun limits as infringing upon the US Constitution's Second Amendment right to bear arms.

Other speakers at the Washington rally included David Hogg, another Parkland survivor and co-founder of MFOL; Becky Pringle and Randi Weingarten, the presidents of the two largest US teachers unions; and Muriel Bowser, the mayor of Washington, DC.

Members of MFOL have spent the week meeting with lawmakers in Washington to discuss gun violence.

Two high school students from the Washington suburb of Silver Spring, Maryland - Zena Phillip, 16, and Blain Sirak, 15 - said they had never joined a protest before but felt motivated by the shooting in Texas.

"Just knowing that there's a possibility that can happen in my own school terrifies me," Phillip said. "A lot of kids are getting numb to this to the point they feel hopeless."

Sirak said she backed more gun restrictions and that the issue extended beyond mass shootings to the daily toll of gun violence.

"People are able to get military-grade guns in America," she said. "It's absolutely absurd."