Officials said he would first have to face justice before any consideration could be shown towards him and that the Vientiane government had no intention of reconciling with him.
He has been sentenced to death in absentia.
Former Hmong General Vang Pao said in Fresno, California on Tuesday that he would like to return to Laos after New Year's and end the drawnout conflict with the communist government.
He was backed by the US Central Intelligence Agency (CIA) in fighting the communist Pathet Lao movement before the fall of Vientiane in 1975 and has lived in exile in the US ever since.
Officials are monitoring news about the ageing Hmong leader and consider his latest move a decoy, the purpose of which is not clear, said Lao Foreign Ministry spokesman Khenthong Nuanthasing.
"If he comes to Laos soon, he must submit to the death sentence that was handed down against him in absentia by the Lao People's Court after the present regime took power in 1975," Khenthong said in a telephone interview from Vientiane.
In Fresno on the occasion of his 80th birthday, Vang Pao told some 1,000 Hmong: "Now is the time for reconciliation [with Laos], to liberate thousands of Hmong trapped in the jungles and stuck in a Thai refugee camp.
"We have to make a change right now. The government of Laos has tried to open the door. We should put something on the table and sit down in peace."
Khenthong said it was government policy to welcome its citizens living abroad who had fled their homes after the events of 1975 but who wanted to return and help rebuild the country.
"But this policy applies to those who were not convicted or did not commit any wrongdoing," he said.
Vang Pao's close aide said an unnamed official connected with a Thai royal project and a politburo member of the Lao People's Revolutionary Party would assist the general with a planned visit to Thailand next month. If the situation is conducive, he plans to cross the Mekong River via the Friendship Bridge in Nong Khai and make a brief visit to his home country.
However, Khenthong said no key member of the ruling party had arranged any such deal for him, since the government in Vientiane "has nothing to deal with him".
"We can develop the country without Vang Pao. We don't need him," he said.
Laos does not see Vang Pao's plans as having any connection with the proposed repatriation of 4,000 Hmong from Phetchabun province, which Thailand is preparing to carry out at the end of this month.
Laos is ready to take them all, but Thailand has not yet informed Vientiane about the huge deportation, Khenthong said.
The Thai military plans to shut down Phetchabun's Ban Huay Nam Khao shelter and force the Hmong to return home, but the international community has urged Bangkok to halt the plan, for fear of the deportees' safety.
Some of the Hmong claim to be close associates of the CIA's secret fighters and fled from suppression at home. Laos and Thailand both regard them as normal economic migrants.