The United States Thursday acknowledged this week's release of political prisoners in Burma. But the State Department says authorities in Rangoon should go further by releasing all political detainees, including democracy leader Aung San Suu Kyi.

The military-led Burmese government freed nearly 250 political prisoners Wednesday in a move widely reported to have been linked to the upcoming meeting in Laos of foreign ministers of ASEAN (Association of Southeast Asian Nations).

At a news briefing here, State Department Spokesman Sean McCormack appeared to downplay the Burmese gesture, acknowledging the prisoner release, but pointedly not welcoming it.

Mr. McCormack said arrests of Burmese democracy supporters continue unabated despite what he said were periodic releases of small numbers of political prisoners, many of whom he said had already completed their sentences.

The spokesman said the United States continues to insist on the release of all Burmese political detainees, and dialogue leading to democratic rule.

"We again call upon Burmese authorities to release Aung San Suu Kyi, U Tin Oo, Hkun Htun Oo, and all other political prisoners immediately and unconditionally, and to engage the democratic opposition and ethnic minority groups in a meaningful dialogue leading to genuine national reconciliation and establishment of democracy," said Mr. McCormack.

Aung San Suu Kyi, the 1991 Nobel Peace Laureate, has been under detention most of the time since her National League for Democracy Party (NLD) won national elections in 1990, but was prevented from taking power by military authorities.

The other leading detainees cited by Spokesman McCormack were U Tin Oo, the vice chairman of the NLD, and Hkun Htun Oo, who heads the Shan Nationalities League for Democracy, the country's second largest party.

There has been renewed focus on the issue of Burmese detainees since last month when Aung San Suu Kyi marked her 60th birthday, under house arrest at her home in Rangoon.

There were statements of tribute to Aung San Suu Kyi from, among others, President Bush and Secretary of State Condoleezza Rice, who officials say will raise the issue of Burma when she visits Thailand early next week as part of the four-nation Asian trip she begins Friday.

State Department officials meanwhile insisted Thursday Secretary Rice intended no snub of ASEAN in deciding not to attend the political dialogue that will follow the July 24 foreign ministers meeting in Vientiane.

U.S. Secretaries of State have taken part in the ASEAN event every year since the early 1980s. But officials say the secretary will not attend this year because of a scheduling conflict related to another foreign trip.

Though details have not been announced, it is understood that Ms. Rice intends to make her first trip as Secretary of State to sub-Saharan Africa later this month and attend a key meeting on U.S.-African trade.

The U.S. delegation to the ASEAN forum will be led by Deputy Secretary Robert Zoellick, who officials stress will pursue a full agenda, including the issue of Burma.

Burma is due to have the rotating chairmanship of ASEAN next year, a prospect that has spurred concern among some other members of the regional grouping as well as the United States and European Union.

The United States, which along with the EU has imposed economic sanctions against Burma, has threatened to boycott ASEAN meetings if Burma assumes the chairmanship without having made major strides on human rights.