Aung San Suu Kyi was detained on May 30 following fighting that left at least four people dead and prompted a crackdown on her National League for Democracy party.
The Nobel peace laureate's whereabouts remain unknown with the junta refusing to produce her in the public. Offices of her NLD party have been shut and other opposition members detained. Other party leaders are under house arrest.
Suu Kyi's detention has drawn sharp criticism from around the world. Exiled opposition figures in Thailand say Suu Kyi may have received head injuries in the May 30 violence, which they say left up to 70 people dead.
The government, however, says she is unhurt and is in custody in a "safe place."
But a U.N. envoy has yet to visit Suu Kyi. The envoy, Razali Ismail, said he was "encouraged" by his meeting Monday with Burma's two top generals in a bid to secure her release.
"I hope I will be able to fulfill one or two of my objectives of my visit here," he said, but refused to confirm if he was given assurances on Suu Kyi's release. Asked if he will be allowed to see her, Razali said: "That's all I can say."
The U.S. State Department says the May 30 violence appears to have been an ambush orchestrated by junta supporters, and that the events suggests the junta has ended efforts at national reconciliation, launched most recently in late 2000 and brokered by Razali in a series of visits.
The Bush administration said it wants Congress to impose more economic sanctions against Burma and was reviewing legislation to prohibit imports from the impoverished country. The United States already bans new investments by U.S. companies.
However, the junta has remained defiant. Khin Nyunt said over the weekend that Burma (which the military dictatorship calls Myanmar) will continue to strive to become a "peaceful, developed and democratic nation" with or without foreign assistance.
Since the crackdown, Washington has tightened visa restrictions against the Burma regime, to cover all officials of the government-linked social organization, the Union Solidarity Development Association, said to have orchestrated rallies against Suu Kyi.
The restrictions previously barred entry only to senior government officials and their immediate families.
Suu Kyi, who won the Nobel Peace Prize for her nonviolent struggle for democracy, spent six years under house arrest in 1989-95. Her party won general elections in 1990 but was blocked by the military from taking power.
Ismail told reporters that he held a one-hour meeting with Deputy Senior Gen. Maung Aye, the regime's No. 2 general, in the presence of the junta's No. 3 Gen. Khin Nyunt, at a Defense Ministry guesthouse.
He later met with the ambassadors of China and Japan but details of the talks were not available.
"Ambassador Razali is working very hard and I hope he will get a good result," the Japanese ambassador, Yuji Miyamoto, told reporters.
Chinese Ambassador Li Jun Jing said he told Razali that his government considers the May 30 events Burma's "internal political affair."