He is to return to Naypyidaw, Myanmar's capital, 385km north of Yangon, for a possible meeting, the UN said.
Gambari "looks forward to meeting ... Than Shwe" before he leaves the region, the UN statement said.
"Where are the peace and human rights defenders of the world (the super powers)? They haven't done enough in this case. Isn't there oil in Myanmar?"
Lost Soldier, Arusha, Tanzania
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The UN said Gambari "conveyed a message" from Ban Ki-moon, the UN secretary-general, when he met Lieutenant-General Thein Sein, the acting prime minister, and Brigadier-General Kyaw Hsan, the minister of information, among other government officials in Naypyidaw.
While these officials have senior positions in the military government, the final say in all decisions rests with Than Shwe, and to some extent Maung Aye.
Gambari was earlier allowed to meet Aung San Suu Kyi, the opposition leader who is under house arrest.
The meeting took place at a government guest house in the commercial capital, Yangon.
The Nigerian-born Gambari was dispatched by Ban to intervene after the government unleashed a military campaign to shut down demonstrations, killing least 13 people and arresting hundreds.
The four days of repression, which has seen live rounds, baton charges and tear gas used against monks, protesters and civilians alike, succeeded in largely shutting down the demonstrations over the weekend.
Sunday's diplomatic developments occurred as thousands of government soldiers locked down Myanmar's largest cities.
Scores of people were arrested overnight, further weakening a flagging uprising to end 45 years of military rule that began on August 19 with protests against fuel price increases.
"There must be a result from this visit," said Razali Ismail, a Malaysian diplomat and Gambari's predecessor as UN special envoy.
"[Gambari] must get a promise from the military that they will not shoot the people who express their views [on the streets]. We cannot let the people down," he said.
Bo Hla Tint, a former politician, told Al Jazeera that people in Myanmar expect the UN to find a solution to the crisis.
"People are expecting Gambari to stay as long as it takes to get tangible results," he said.
A Japanese envoy also arrived in Myanmar on Sunday to urge the military government to thoroughly investigate the killing of a Japanese journalist during an anti-government rally and not to use force to end the protests.
Kenji Nagai, 50, a video journalist, was fatally wounded in Yangon on Thursday, apparently shot by a soldier firing at point-blank range.
"One [purpose] is to make sure there is a full investigation into the dreadful incident and to ensure the safety of Japanese nationals," Mitoji Yabunaka, deputy foreign minister, said at Narita airport.
While the international community exerts diplomatic pressure, Myanmar's military government continues to tighten its hold over the streets.
Andrew Kirkwood of the Save The Children told Al Jazeera that the government seemed to be in control of Yangon on Sunday.
"But there is an atmosphere of high tension here," he said.
|Aung San Suu Kyi remains an icon of |
democracy for many in Myanmar [AFP]
Dissidents said on Sunday they were looking for alternative venues to gather, away from the thousands of security forces massed in Yangon.
"We plan to go ahead with our movement," a source involved in the protests said.
Troops have blockaded many big monasteries, including in Mandalay, and monks are only allowed to move around in small groups.
Myanmar's main internet connection has been cut since Friday, drastically reducing the flow of video, photos and first-hand reports of the violence which have helped inform the world of the crisis.