China has repatriated all 31 North Korean refugees it arrested last month despite international pressure against the move, refugee advocates in South Korea said Friday.

The advocates say the refugees could suffer abuse or even execution for fleeing North Korea during the mourning period for its late leader Kim Jong-Il.

Do Hee-Yun, head of the Seoul-based Citizens' Coalition for Human Rights of Abductees and North Korean Refugees, said the refugees left North Korea in three separate groups and were arrested in different places in China.

"They were returned to the North clandestinely over the past two weeks," Do told AFP. "They are likely to be severely punished as they fled the North during the mourning period."

The North has been in mourning since Kim Jong-Il died of a heart attack on December 17. He was succeeded by his youngest son Kim Jong-Un.

Rumors are common near the border that the new leader issued a shoot-to-kill order against people attempting to cross the border during the mourning period and also called for stern punishment for their relatives, Do said.

North Korea has in the past treated its citizens who crossed the border to find food with relative leniency while punishing severely anyone who attempted to flee to the South, according to the dissident group North Korea Intellectuals Solidarity.

More recently, all refugees are now treated as traitors worthy of severe retribution, the group of North Korean defectors based in Seoul said.

Seoul has repeatedly urged Beijing to treat people fleeing North Korea as refugees and not to repatriate them. China says the group sent back in recent days consists of economic migrants and not refugees deserving protection.

US Secretary of State Hillary Clinton, when asked about the issue during a joint news conference in Washington with South Korean Foreign Minister Kim Sung-Hwan, said America opposed sending refugees back to countries where they face retribution.

Clinton did not comment directly on accounts of repatriation but said: "We urge every country to act according to international obligations" including the 1951 UN refugee convention and the 1967 protocol.

"The United States shares the concerns by both the government and the people of the Republic of (South) Korea about the human rights situation in North Korea and the treatment of North Korean refugees," the chief US diplomat said.

"We believe that refugees should not be repatriated and subjected once again to the dangers that they fled from," Clinton said.

She said that Glyn Davies, the US special representative on North Korea policy, raised concerns about the refugees with senior officials during a visit to China last month.

"We urge all countries in the region to cooperate in the protection of North Korean refugees within their territories," Clinton added.

The UN refugee agency had also urged Beijing not to send back the North Koreans. Rights watchdog Amnesty International says returnees are sent to labor camps where they are subject to torture.

US lawmaker Chris Smith, co-chair of the Congressional Executive Commission on China, earlier urged Washington to link Pyongyang's treatment of refugees to its decision last week to deliver 240,000 metric tons of food aid to the country.

More than 21,700 North Koreans have fled to the South since the 1950-1953 war, the vast majority in recent years. They typically escape on foot to China, hide out and then travel to a third country to seek resettlement in the South.