With a new US school year beginning, President Joe Biden on Wednesday warned governors who oppose student mask requirements that they could face legal action for intimidating educators seeking to protect children against Covid-19.

In the latest political flashpoint over the coronavirus pandemic, Republican governors in Florida and Texas, two of the country's largest states, have rejected recommendations by health authorities to require that students wear masks when they return to the classroom.

Florida's Board of Education raised eyebrows when it voted this week to slap punishments on two school districts that instituted mask mandates in defiance of Governor Ron DeSantis.

Biden did not mention DeSantis by name, but his comments in a White House address appeared squarely aimed at the governor, who is believed to harbor presidential ambitions.

"Unfortunately... some politicians are trying to turn public safety measures -- that is, children wearing masks in school -- into political disputes for their own political gain," Biden said. "They're setting a dangerous tone."

As a response, the president said he instructed Secretary of Education Miguel Cardona to use "legal action, if appropriate, against governors who are trying to block and intimidate local school officials and educators."

"If you aren't going to fight Covid-19, at least get out of the way of everyone else who's trying."

Biden also slammed protesters who have interrupted school board meetings, singling out angry parents in Tennessee who he said threatened doctors and nurses making the case for masking children in schools.

"The intimidation and threats we're seeing across the country are wrong. They're unacceptable," Biden said.

The United States is facing a resurgence of Covid-19 infections, as the Delta variant spreads.

Along with fierce opposition to mask mandates in certain quarters, the country's mass vaccination program also faces some resistance, particularly in politically conservative regions in the South and Midwest.