The United States renewed its call on Burmese military authorities Thursday to release democracy leader Aung San Suu Kyi and other members of her political party detained after a clash with government supporters last Friday. The State Department says U.S. policy towards Burma is under review in light of the latest events there.

The State Department says the clash in northern Burma, in which Aung San Suu Kyi was reportedly injured, appears to have been a "pre-meditated ambush" staged by what it terms "government-affiliated thugs."

It is reiterating its call on authorities in Rangoon to immediately release the democracy leader and other detained supporters, and to provide all necessary medical attention to those hurt in the assault on her motorcade.

In a written statement, State Department spokesman Philip Reeker said U.S. diplomats inspected the scene of the attack, and concluded from debris and other evidence that it was a major clash that could easily have produced serious injuries to large numbers of people.

The Burmese government has said four people died in the incident, while exiled Burmese dissidents contend the death toll was 70 or 80.

Military officials have said Aung San Suu Kyi was taken into "preventive custody" after the attack and was not hurt, though diplomatic sources said she sustained facial and shoulder injuries from objects thrown at her car.

Spokesman Reeker called the continued detention, in isolation, of Aung San Suu Kyi and her colleagues "outrageous and unacceptable" and demanded a "full accounting" of the casualties in the attack, which is seen by U.S. officials as having dealt a major setback to hopes for an early democratic transition in the country.

Mr. Reeker said the United Nations special envoy for Burma Razali Ismail, due to arrive in Burma Friday, must be allowed to meet privately with Aung San Suu Kyi and other opposition leaders. He said if he is not allowed to do so, the United States will need to "re-evaluate the utility" of the U.N. effort to support Burmese national reconciliation.

The latest events have prompted the introduction of bipartisan legislation in the Senate to tighten U.S. sanctions against the Burmese military government until it ends human rights abuses and transfers power to a popularly elected civilian government.

Republican Senator Mitch McConnell, sponsor of the measure along with Democrat Diane Feinstein, told reporters it reflects growing concern about the status of Aung San Suu Kyi, whose party won national elections in 1990, but has been prevented from taking office.

"Clearly, this Nobel Peace Prize-winner patriot, who has spent so much of her life trying to establish democracy in Burma, is in grave danger," he said, "and we are no closer to recognition of the election than we have been at any time over the last 13 years."

Senator McConnell said one "silver lining" or benefit of the latest crackdown is that it has put the Burmese situation on newspaper front pages, and that the junta will no longer be able to escape international scrutiny of its activities.

He said he hopes the Bush administration will lead an international effort to force democratic change in Burma. He called on Secretary of State Colin Powell to put the issue at the top of his agenda when he attends a dialogue with foreign ministers of ASEAN, the Association of Southeast Asian Nations, later this month in the Cambodian capital, Phnom Penh.

Officials here said they would study the McConnell-Feinstein bill before offering comment. The United States already has extensive sanctions in place against Burma, including an arms embargo, a ban on new U.S. investment, and a travel ban on senior Burmese officials.

They say overall U.S. policy toward Burma is under "active review" in light of the current situation.