The military on Friday defended the deportation of two Chinese refugees to Beijing last weekend in a bid to deflect criticism from the international community.
It also claimed the activists "were involved in human trafficking".
The refugees were deported after they were arrested for illegal entry into Thailand, National Security Council secretary-general Thawip Netniyom said.
Gen Thawip said that apart from the illegal entry charge, the Thai government was informed by China that the men — Dong Guangping and Jiang Yefei — were anti-Chinese government activists and were allegedly involved in human trafficking in their home country.
"The UNHCR [the United Nations High Commissioner for Refugees] only has information that they are [anti-Chinese government] activists. It does not know that they have [allegedly] committed human trafficking offences," he said.
He said Deputy Prime Minister Prawit Wongsuwon on Friday sought to clarify with UNHCR representatives in Thailand the reasons why Thailand needed to deport them.
"We considered the matter carefully and stuck to laws and international agreements," Gen Thawip said.
Mr Dong and Mr Jiang were repatriated last weekend even though the UNHCR informed key Thai government agencies on Nov 10 the two had been accepted for refugee resettlement to Canada and would be departing within days.
Government sources said Thailand was taken aback after underestimating the effect of its actions and said lessons "were never learned by the military regime". The reference was to the earlier outcry over the deportation of 109 Uighurs to China.
The Thai government has come under some heavy flak from Amnesty International, the UNHCR, Human Rights Watch and the United States for the forced repatriation to China of the two men.
On Thursday, Glyn Davies, the US ambassador to Thailand, expressed his nation's "disappointment" with the Thai authorities' decision, particularly since Thailand has obligations to the UNHCR.
The Office of the United Nations High Commissioner for Human Rights (OHCHR) on Friday issued a statement to condemn the Thai government's move.
"We have expressed our concern to the Government of Thailand about the deportation which comes just over four months after we voiced concern over the government's deportation of 109 ethnic Uighurs to China," the OHCHR said in a lengthy statement issued in Geneva.
The principle of non-refoulement, which prohibits the return of a refugee to a country where they are likely to face persecution or torture, is contained in a convention that Thailand is signatory to, the OHCHR said.
The UNHCR said the two men had been due to depart for a third country where they were to be resettled along with their families.
The UN body said reasons for the deportation remain unclear.
Since their deportation, other family members who were in Thailand have left the country for third-country resettlement.
"We strongly urge the Thai government to stop deporting individuals, including potential refugees and asylum seekers, to countries where there are substantial grounds to believe that they would face an imminent risk of grave human rights violations, including torture," the OHCHR said.
"We further urge the government to put in place an effective system of review of all cases before deportation happens to ensure that there are no serious risks of torture or ill-treatment."
Human Rights Watch also condemned the move.
“Thailand’s forced return of these two human rights activists into harm’s way in China after being explicitly told that they were refugees is cruel as well as unlawful,” said Sophie Richardson, China director at Human Rights Watch.