Ibrahim Gambari, addressing the UN Security Council after a four-day visit to Burma, called for the release of all political prisoners there and voiced concern at reports of continuing government abuses after last week's protests.
"Of great concern to the United Nations and the international community are the continuing and disturbing reports of abuses being committed by security and non-uniformed elements, particularly at night during curfew, including raids on private homes, beatings, arbitrary arrests, and disappearances," Mr Gambari told the Council.
He said Burma's Government must recognise that what happened there "can have serious international repercussions".
The United States said it would propose sanctions at the 15-member Council if Burma did not "respond constructively" to international concerns, but success seemed unlikely with veto-wielding China firmly opposed to such action.
In a warning to the world body, Burma urged the United Nations to take no action that would harm its "good offices" role in defusing the crisis there.
Offer of talks
The opposition in Rangoon dismissed the junta's offer of talks with Ms Suu Kyi as effectively asking her to abandon the campaign for democracy that has kept her in detention for 12 of the last 18 years.
"They are asking her to confess to offences that she has not committed," said Nyan Win, spokesman for the Nobel peace laureate's National League for Democracy (NLD), whose landslide election victory in 1990 was ignored by the generals.
Than Shwe, head of the latest junta in 45 unbroken years of military rule of Burma, set out his conditions for direct talks at a meeting with Mr Gambari last Tuesday, state-run television said. It said Ms Suu Kyi must abandon "confrontation" and give up "obstructive measures" and support for sanctions and "utter devastation", a phrase it did not explain.
Nyan Win demanded Ms Suu Kyi be allowed to respond in public.
That is unlikely. The only time Ms Suu Kyi has been seen in public since she was last detained in May 2003 was during one of the monk-led demonstrations when protesters were allowed through the barricades sealing off her street.
People who applauded the protest marches could face two to five years in jail, said Win Min, who fled to Thailand in 1988 as the army crushed an uprising at the cost of around 3,000 lives.
Leaders could face 20 years, he said.
The Norway-based opposition Democratic Voice of Burma quoted relatives as saying about 50 students who demonstrated in Mandalay had been sentenced to five years hard labour.
Casualties 'much higher'
Mr Gambari, adressing an open meeting of the Council whose audience included around a dozen Buddhist monks in robes, said there were unconfirmed reports that casualties were much higher than the handful reported by the Government.
The junta says 10 people were killed in the crackdown on the biggest challenge to the junta in nearly 20 years, though Western governments say the toll is likely to be far higher.
Addressing the Council, UN Secretary-General Ban Ki-moon called for "bold actions" by the military government toward democratisation and respect for human rights.
"The use of force against peaceful demonstrators is abhorrent and unacceptable," he said.
China's UN Ambassador Wang Guangya, however, reiterated Beijing's view that Burma posed no threat to international peace and security, a condition for Security Council action. China borders Burma and is one of the country's few allies and major trading partners.
Pressure, he said, "will not help address the problem but might lead to mistrust and confrontation".
Burma's UN Ambassador Kyaw Tint Swe urged the UN not to take action in the Security Council and said many of those detained had now been released.
"To date ... a total of 2095 people, including 722 monks, have been released," he said. "More releases will follow."
Despite China's opposition, US Ambassador Zalmay Khalilzad said Washington was prepared to introduce a resolution in the Security Council imposing sanctions.
"We must all be prepared to consider measures such as arms embargoes," Khalilzad told the Council, urging Burma's neighbors to exert the maximum pressure to get the military government there to cooperate with Mr Gambari's efforts.
In Washington, the United States called on the junta to talk to Ms Suu Kyi without conditions, and US charge d'affaires Shari Villarosa went to the new capital, Naypyidaw, to urge it to begin a "meaningful dialogue" with opposition groups.
"It was not a terribly edifying meeting from our perspective," said State Department spokesman Sean McCormack, adding that Villarosa's meeting with Deputy Foreign Minister Maung Myint produced no breakthroughs.
Singapore, a leading investor in Burma, said sanctions should not be ruled out but questioned their impact against the ruling junta and the damage they might do to future reconciliation talks.
"This should not be an excuse for delaying necessary steps forward," Singapore's UN Ambassador Vanu Gopala Menon said at the Council debate.
"But neither do we want a Yugoslavia in South-East Asia," he added, referring to the Balkan country's disintegration amid ethnic warfare in the 1990s.