US Secretary of State Hillary Clinton vowed Wednesday never to accept a peace agreement in Afghanistan that rolls back women's rights, despite reaching out to the Taliban for talks.

The United States is seeking a political settlement that would allow NATO forces to leave by the end of 2014, ending the longest-ever US war as it grows increasingly unpopular with the US public.

But Clinton, a longtime advocate for women's rights, said the United States would not allow a return to conditions under the Taliban regime that barred women from the workplace and school before the US invasion toppled it in 2001.

"We will not waiver on this point -- any peace that is attempted to be made by excluding more than half the population is no peace at all. It is a figment that will not last," Clinton said.

The top US diplomat said that a "red line" for the United States was that the Taliban accept Afghanistan's constitution, which protects women's rights.

"Many are worried that in whatever future negotiations that might occur, women, their rights, their roles, their concerns will be sacrificed and the old days will return," Clinton said.

"The United States cannot and will not let that happen.

"Let there be no doubt -- even as the US role in Afghanistan changes in the next few years of transition, we will continue to stand with and work closely with Afghan women," she said.

Clinton was speaking at a luncheon to mark the 10th anniversary of the US-Afghan Women's Council, an institute set up at Georgetown University that looks to promote the rights of Afghan women and children.

The Taliban had set up an office in the Gulf state of Qatar to pursue dialogue with the United States. But the militants announced last week that they were suspending the contacts due to a row over a prisoner swap.

Clinton, meeting earlier with Afghan Foreign Minister Zalmai Rassoul before the two attended the women's luncheon together, said that the United States was still open to talks with the Taliban.

"What the Taliban do is up to them. We have been clear, we are prepared to continue discussions and our goal is to open the door so that Afghans can be negotiating among and between themselves," Clinton said.

Clinton also made a fresh statement of regret on behalf of President Barack Obama's administration for a US soldier's massacre of 16 Afghan civilians, most of them women and children.

"This has been very personally painful to me and to the president. It does not represent who the United States is, who the American people are," she said.

The Afghan foreign minister said that his country has made major advances in women's rights, saying that girls -- forbidden from school just a decade ago -- now constitute about 40 percent of schoolchildren.

Women also make up 28 percent of members of parliament, 30 percent of schoolteachers and about one-quarter of government employees and medical workers, Rassoul said.

"These gains and the collective change they represent are historic and a source of real, genuine pride for all Afghans," he said.

But he acknowledged that "far too many" Afghan girls do not have the chance to go to school and that women "continue to suffer terrible violence."

"Our gains are fragile and depend upon a smooth and successful transition up to and beyond 2014," Rassoul said.

Former first lady Laura Bush, who serves as an honorary adviser to the US-Afghan Women's Council, voiced concern over violence against woman and about the "limited" number of women involved in the peace process.

"No one wants to see Afghanistan's progress reversed or its people returned to the perilous circumstances that marked the Taliban's rule," Bush said.