Burma's military rulers have told United Nations human rights envoy Paulo Sergio Pinheiro he can begin a five-day visit to the country on Sunday.
Mr Pinheiro has not visited Burma since November 2003
Mr Pinheiro, banned from Burma since 2003, said the invite was a "positive indication" from the generals.
But he warned: "If they don't give me full co-operation, I'll go to the plane, and I'll go out."
The announcement comes as another UN envoy, Ibrahim Gambari, continues talks with senior political figures there.
Mr Gambari arrived in Burma on Saturday for his second visit since September's anti-government protests were brutally suppressed.
Mr Pinheiro - known officially as the UN's special rapporteur on human rights in Burma - said he had received an invitation from the generals to visit between 11 and 15 November.
"The special rapporteur notes that this invitation sends a positive indication of the desire of the authorities to co-operate with his mandate," his office said in a statement.
Mr Pinheiro has repeatedly requested access to the country, but has been refused entry since 2003.
Last month Burmese Foreign Minister Nay Win wrote to the UN suggesting Mr Pinheiro should arrive in mid-November - before a meeting of the Association of South-East Asian Nations (Asean).
Analysts believe the junta is trying to forestall criticism of its handling of the protests from Asean leaders, who previously expressed "revulsion" at the regime's actions.
A sharp rise in fuel prices triggered protests in mid-August that snowballed into mass demonstrations led by Buddhist monks.
The junta crushed the dissent by opening fire on crowds and detaining thousands of people.