Brigadier-General Kyaw Hsan met Gambari on Friday, reporting later that the military government had done enough to hold dialogue with Suu Kyi.
Suu Kyi, under house arrest for 12 of the past 18 years since her National League for Democracy (NLD) won, by a landslide, elections in 1990, says she is "not satisfied" with progress on negotiations.
She was not allowed to participate in the government-led commission that prepared guidelines for the new constitution. The government now says it is impossible to amend it.
Last September, Buddhist monks led street protests sparked by political discontent and rising prices. According to the United Nations, at least 31 people died when police put down the demonstrations. The toll could be far higher.
"The constitution has already been drafted and it should not be amended again"
Kyaw Hsan, information minister
If the elections go ahead, they will be the first since 1990 and Suu Kyi's win, which has never been recognised by the military.
A new law governing the referendum also limits her party's ability to campaign, criminalising public speeches and leaflets about the vote.
World powers have decried Myanmar's plans because they fail to include the NLD.
Kyaw Hsan said on state television: "The constitution has already been drafted and it should not be amended again."
He said the NLD had been invited to take part in the constitutional talks, but had refused to attend. The party boycotted the talks in protest at Suu Kyi's house arrest.
The minister also accused Gambari of bias in favour of Suu Kyi after he released a statement from her following his last visit to the country in November.
Kyaw Hsan wrote: "We are very astonished and dismayed for your involvement in this matter.
"Sadly, you went beyond your mandate. Hence, the majority of people are criticising it as a biased act. Some even believe that you prepared the statement in advance and released it after co-ordinating with Daw Aung San Suu Kyi.
"The statement was dangerous to the degree of hurting the prevailing peace and stability of the nation."
He also said that if Gambari tried to force the country to meet Western calls for reform, "we are concerned that your task of offering impartial advice may be undermined".
The NLD has said that the public would not accept the government's charter, but has stopped short of calling for a boycott or urging a "No" vote.
Gambari was to meet NLD leaders on Saturday, but no meeting with Suu Kyi has been confirmed.
Gambari has tried to open a dialogue between her and the government, and after his first mission, the military leaders appointed a liaison officer to meet Suu Kyi.
However, Senior General Than Shwe, the country's leader, did not meet Gambari on his last visit.
Myanmar is widely criticised for its poor human rights record and failure to hand over power to Suu Kyi's party. Myanmar has been under military rule since 1962.