TEHRAN — In a major shift, Iran announced Saturday that women would be allowed to attend big sporting events, reversing a rule that had barred them from entering stadiums to watch matches attended by men.

The announcement, following criticism from international sport federations and protests by Iranian women and women’s rights activists, appeared to have been timed to coincide with the news of a breakthrough in the negotiations over Iran’s nuclear program.

A Ministry of Youth Affairs and Sports official told the state-run Islamic Republic News Agency that women and their families would be allowed to attend most athletic events, except for those of “masculine” sports, like wrestling or swimming, during which male athletes wear uniforms or suits that cover little of their bodies.

Women will most likely be assigned to special sections in the stadiums, while mixed seating will be available for families.

The decision, if put in effect, will be a big victory for President Hassan Rouhani, who has been trying to allow Iranians more personal freedoms and to adjust laws that are seen as outdated as Iran becomes an increasingly urbanized society. Iran’s National Security Council, which is supervised by the Interior Ministry, confirmed the change two weeks ago, but the official announcement was delayed until Saturday, two days after Iran reached an agreement with the United States and five other world powers on the parameters for an accord on Iran’s nuclear program.

Although challenges to entrenched policies and conservative sensibilities often encounter resistance from hard-liners, the news cheered activists working for change. “I am very happy,” said Najiyeh Allahdad, a 38-year old activist who has campaigned for women to be allowed into stadiums. “We have done all we could to get our rights back. This should have happened some time ago. It is now clear for me that this government is really trying hard to improve our lives.”

Shiite Islam, the state religion in Iran, generally tries to separate men and women. But compared with countries like Saudi Arabia, where the segregation of the sexes is widely enforced, Iran takes a more pragmatic approach. For instance, buses and trains have special compartments for women, but shared taxis do not.

During official and religious gatherings, men and women are allowed to mix, but at most universities, they are not. Many of these measures are not codified in laws but are results of decisions made by bodies like the National Security Council in consultation with religious leaders.

Usually, the Supreme Cultural Revolution Council, which determines Iran’s major cultural policies, must confirm such a major change. It is unclear whether it has done so in this case.

Iran was one of the few countries that barred women from sporting events, including soccer, an immensely popular sport in Iran. Last year, it also barred them from attending volleyball matches, prompting an angry reaction among women.

Women’s rights activists protested and demanded equal treatment. An Iranian-British activist, Ghoncheh Ghavami, was arrested after trying to attend a men’s volleyball match in June. She was convicted and sentenced to a year in jail and a two-year travel ban. But last week, an appeals court dismissed the charges against Ms. Ghavami, who had been released on bail after five months in prison.

“I want to shout inside the stadiums again,” said Monireh Davari, 23, a volleyball fan. “It was our right to be there.”

With the ban lifted, Ms. Davari said she hoped that Iran would start hosting international sporting events. “I want to see the foreign fans, mix with them and be friends with people from all over the world,” she said.

The international soccer and volleyball federations had objected to the ban, threatening a boycott of Iranian teams if it was not lifted. In March, Sepp Blatter, the president of the soccer federation, called the situation “intolerable” and complained that Mr. Rouhani had not done enough to change it.

“Nothing has happened,” Mr. Blatter wrote in a letter published in the federation’s weekly magazine. “A collective stadium ban still applies to women in Iran, despite the existence of a thriving women’s football organization. This cannot continue. Hence my appeal to the Iranian authorities: Open the nation’s football stadiums to women.”

In March, the United Arab Emirates was chosen over Iran to host the 2019 Asian Cup in the wake of criticism of Iran’s policy.

Ms. Davari said it was clear that international pressure had played a role in Iran’s decision to reverse the policy. “Iran was missing out on so many opportunities,” she said. “This had to change.”