Gambari is on his second visit to Myanmar in a month in an effort to persuade Myanmar's government to adopt democratic reforms.
Gambari met Lieutenant-General Thein Sein, Myanmar's prime minister, in the new capital Naypyidaw on Wednesday.
The UN said in a statement late on Wednesday that Gambari gave Thein Sein a letter from Ban Ki-moon, the UN's secretary-general, to pass on to Than Shwe, the country's senior general.
Ban has already expressed concern that Gambari has not been permitted to visit Than Shwe during his visit.
|Buddhist monks led popular pro-democracy |
protests in Myanmar in September [AFP]
"Mr Gambari stressed that a return to the status quo before the crisis would not be sustainable," the UN statement said.
Gambari will meet Aung San Suu Kyi, who remains under house arrest in Yangon, on Thursday, shortly after meeting senior members of her National League for Democracy (NLD) in Naypyidaw.
In comments published in the New Light of Myanmar, Kyaw Hsan said the government would not be pressured into making democratic reforms.
"If you wish to see democracy flourishing in Myanmar, you should try to persuade other nations to co-operate with us in assisting [us with] the task," he said.
"Here, what we would like to say is that we will welcome positive co-ordination and co-operation for Myanmar affairs, but will never accept any interference that may harm our sovereignty."
State media have indicated the government is only willing to adopt its own seven-stage "roadmap to democracy".
The roadmap has been criticised by Western governments as a method to keep the military generals in power.
Gambari appealed on Wednesday for restrictions on Aung San Suu Kyi and all political prisoners to end, the UN and Kyaw Hsan said.
However, Myanmar's rulers say that Aung San Suu Kyi must first abandon her support for international sanctions against the government.
Aung San Suu Kyi led the NLD to victory in a general election in 1990, but Myanmar's generals have not allowed her party to take office.