California has begun stockpiling abortion pills, the governor announced Monday, joining other liberal states in fighting a conservative-led effort to restrict access to reproductive care in the United States.

The move comes after a federal judge last week ordered a freeze on the distribution of mifepristone, a medication deemed safe and effective by national regulators more than 20 years ago.

Governor Gavin Newsom said California, the most populous state in the nation, had secured two million doses of misoprostol, a drug usually taken in combination with mifepristone, but which can be taken alone to induce a safe and effective abortion.

"In response to this extremist ban on a medication abortion drug, our state has secured a stockpile of an alternative medication abortion drug to ensure that Californians continue to have access to safe reproductive health treatments," Newsom said.

"We will not cave to extremists who are trying to outlaw these critical abortion services. Medication abortion remains legal in California."

Massachusetts Governor Maura Healey, also a Democrat, said Monday her state has begun stockpiling mifepristone, with a year's worth of doses for the state already in hand.

"We are not going to let one extremist judge in Texas turn back the clock on this proven medication and restrict access to care in our state," Healey said.

Last week, Washington's Democratic governor, Jay Inslee, announced his state had already received three years-worth of mifepristone.

On Monday the US Department of Justice asked an appeals court to freeze the ruling by a federal judge in Texas, Matthew Kacsmaryk, an anti-abortion campaigner who was appointed by former president Donald Trump.

Kacsmaryk's edict came the same day as a judge in Washington state ordered that the Food and Drug Administration be prohibited from pulling access to mifepristone.

The conflicting judicial rulings -- from two politically different states -- illustrate the divide in US society on the issue of abortion.

While polls repeatedly show a clear majority of Americans support continued access to safe abortion, conservative groups have sought to limit what had previously been a right enshrined in law.