Myanmar's government appears to have ignored international calls for a peaceful end to what as small-scale protests against rapid fuel price rises in August and have grown into a mass uprising led by monks.
Speaking in Singapore on Saturday, Gambari said he was going "to deliver a message from the secretary-general to the leadership, a message that is very much by the Security Council and Asean."
"I look forward to a very fruitful visit so that I can report progress on all fronts."
On Saturday, there were fewer people on the streets of Yangon, the country's largest city although some protests continued.
"I think all the people of Myanmar must act to get democracy for a better life"
aprat_1992, Denpasar, Indonesia
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Selena Downes, Al Jazeera's correspondent in Bangkok, said: "If you believe state-run media reports. .. peace and stability has been restored on the streets of Yangon.
"That is at odds with the pictures we've been seeing."
Hundreds were arrested overnight, key religious sites sealed off and monasteries surrounded to prevent Buddhist monks from leading more demonstrations.
Internet links were restored early on Saturday after they were cut the previous day, preventing pictures and video footage of soldiers chasing protesters reaching the outside world.
Few monks took part in the much smaller protests on Friday around the barricades.
People in Yangon said many young monks were evading arrest by casting off their maroon robes and sheltering in houses disguised as laymen.
Japanese newspapers on Saturday said Tokyo will urge Myanmar to punish soldiers responsible for killing a Japanese journalist while cracking down on anti-government protests.
Kenji Nagai, 50, a video-journalist for Tokyo-based APF News, was killed when the government sent troops to quell protest in Yangon on Thursday.
About 80 demonstrators rallied outside the Myanmar's embassy in Tokyo, carrying pictures of Aung San Suu Kyi, the imprisoned pro-democracy leader, and what was believed to be Nagai's body lying on the road against the backdrop of people rushing away from troops.
The deputy foreign minister of Japan, Mitoji Yabunaka, is scheduled to visit Myanmar on Sunday to deliver the demand to the government, the Yomiuri Shimbun said, quoting government sources.
Japan, one of the leading donors to Myanmar, will also consider a ban on Japanese investment in the country after receiving its reaction to the demand, the daily newspaper said.
Tokyo in 2003 suspended low-interest loans for major projects, such as infrastructure, to protest the continued detention of pro-democracy leader Aung San Suu Kyi.
Official aid (2004): $121m
China, India and Japan are key contributors.
Black market: According to most estimates, the black economy matches its official counterpart.
(Sources: Asian Development Bank, 2007 Key Indicators, Reuters, UNDP, UNODC, Global Witness)
But Japan says aid continues for emergencies and humanitarian purposes.
China, the military government's main ally, publicly called for restraint for the first time on Thursday. But at the United Nations, China has ruled out supporting sanctions or a UN condemnation of the government's use of force.
The Association of South East Asian Nations (Asean), which rarely criticises a member directly, expressed "revulsion" at the crackdown.
Gambari, representing Ban Ki-moon, the UN secretary-general, and Asean, was to fly straight on to Myanmar's new capital, Naypyidaw, as soon as he arrives in Yangon later on Saturday, a diplomatic source said.
What the UN's special envoy will be able to achieve remains in question.
Downes said: "There is hope that he's able to bring all groups together to hold some negotiations."
George Yeo, Singapore's foreign minister said: "He's the best hope we have. He is trusted on both sides.
"If he fails, then the situation can become quite dreadful."