Two more women have died after using the abortion pill RU-486, regulators said Friday in a warning that brought renewed calls for pulling the controversial drug from the market.

The organization that provided the pill to the two women said it would immediately stop disregarding the approved instructions for the pill’s use.

The Food and Drug Administration warned doctors to watch for a rare but deadly infection previously implicated in four deaths of women who had taken the drug. The drug, also called Mifeprex or mifepristone, has not been proved to be the cause in any of those cases.

Nor has the FDA confirmed the cause of the latest two deaths. However, in one of them, the woman’s symptoms appeared to resemble those in the cluster of four cases in California where the women died from an infection of the bloodstream, or sepsis. Those women did not follow FDA-approved instructions for the pill-triggered abortion, which requires swallowing three tablets of one drug, followed by two of another two days later.

Instead of swallowing the final two tablets, the second course of pills was inserted vaginally in the four women, an “off-label” use that studies have shown effective and that has been recommended by a majority of the nation’s abortion clinics. That use does not have federal approval, though studies have indicated it produces fewer side effects.

It was not immediately known if the second course of pills had been inserted vaginally in the two latest women to die, an FDA spokeswoman said. She declined to be identified, saying she was not authorized to speak publicly about the issue.

Two Senate abortion foes, Republicans Jim DeMint of South Carolina and Tom Coburn of Oklahoma, urged passage of legislation that would suspend sales of RU-486 until the Government Accountability Office reviews how the FDA approved the pill.

Meanwhile, Planned Parenthood Federation of America Inc. said it would immediately stop recommending vaginal insertion of the final course of pills. Four of the women who died, including the latest two, received the pills at Planned Parenthood-affiliated clinics, said Dr. Vanessa Cullins, the organization’s vice president for medical affairs. Planned Parenthood estimates RU-486 has been used 560,000 times in the U.S. since it was approved.