UNITED NATIONS — Burma’s ruling junta yesterday arrested a prominent activist, while at the United Nations the Security Council gathered to discuss the U.N. envoy to Burma’s recent failure to meet with the country’s leading dissident, Aung San Suu Kyi.

Nilar Thein, leader of a dissident group known as the 88 Generation Students, was detained by Burmese security forces after spending a year in hiding following the arrest of her husband, Kyaw Min Yu. “The arrest — and the huge increase in arrests over the past 30 days — directly defies the U.N. Security Council’s demand that the military regime release all political prisoners,” the Washington-based U.S. Campaign for Burma said in a statement.

Ms. Thein had written about the dissonance between the United Nations’ lofty goals and the junta’s defiance of them. When Secretary of State Rice hosted a meeting at the Security Council on women, peace, and security in June, the activist wrote, “Will they remember Daw Aung San Suu Kyi and the women of Burma who are suffering all forms of abuse by the military junta?”

Taking aim at the failure of U.N. envoys to challenge the generals, Ms. Thein added: “The appeasement policy of some bureaucrats is shameful. Effective and urgent action from the U.N. Security Council is necessary to help the women in Burma. No more debate. Take action. Please let me be happily reunited with my daughter.”

Ms. Thein was forced to leave her infant daughter with her parents when she went into hiding.

Earlier this month, Ms. Suu Kyi, 63, who has been under house arrest since her National League for Democracy won a 1990 election in a landslide but was not allowed to take power, turned away Ibrahim Gambari, who was making his fifth visit to Burma as U.N. envoy in two years. Still, Secretary-General Ban said the Nigerian diplomat’s trip was not a failure. “If you talk about failure, then if we stop making progress through all possible diplomatic means, that should be viewed as a failure. I continue to make progress,” he said.

U.N. diplomats, on the other hand, described Ms. Suu Kyi’s public snub as a sign of her frustration with his mission. Yesterday, Mr. Gambari was unable to explain to members of the Security Council why the Nobel Peace Prize laureate had declined to see him. “To be honest with you, I don’t know, because this is not consistent with her previous relations to me,” he told reporters.

Ms. Suu Kyi’s party “has said some things,” expressing her dissatisfaction that this process, including Mr. Gambari’s visits, has “not produced concrete results,” the American ambassador to the United Nations, Zalmay Khalilzad, said.

The British ambassador, John Sawers, added that Ms. Suu Kyi clearly meant to convey a message.

The Burmese opposition leader “can’t come here to the Security Council and set out her concerns,” Mr. Sawers said. “She’s locked up. So she needs to be able to convey her messages in different ways. We need to understand the frustration that she and her supporters, her party, and indeed the people of Burma are feeling at the lack of progress there. Let’s listen to that.”

In a letter to Mr. Ban last week, several members of Ms. Suu Kyi’s party requested that they be allowed to represent Burma at the upcoming U.N. General Assembly session, instead of the junta’s envoys. Mr. Ban has not yet commented on the request.

Mr. Gambari yesterday declined to criticize the constitutional referendum, described by President Bush and others as a “sham,” that the junta conducted in May, days after a powerful cyclone killed more than 100,000 Burmese citizens. “That is for the people of Burma to decide,” Mr. Gambari said of the referendum. “We were not there to observe the process. How can we judge the outcome?”