A North Korean man has pleaded with the Chinese president Xi Jinping not to forcibly repatriate his wife and young son, saying they face imprisonment or death if sent home.
The woman and her four-year-old son are understood to have been among a group of 10 North Koreans detained in China last week after secretly crossing the border.
The man, who asked to be identified only as Lee, fled to South Korea in 2015. He recorded his plea in a video message which was passed to the BBC.
He said his wife and son would "either face execution or wither away in a political prison camp" if sent back to North Korea.
"I wish China's Xi Jinping and US President Donald Trump would think of my child as their grandchild and send my son to the free country, South Korea," he said.
"Please help us. Save my family from repatriation. As the father, I beg the two leaders to help my family. Please help us."
He said he was haunted by images of his young son in detention.
"I can almost hear my baby calling my name," he said. "I can see my baby in that cold cell, crying out for his father. I can't just stand by doing nothing."
The group of 10 defectors was arrested in a raid on a safe house in Shenyang in Liaoning province, north-east China, on 4 November.
China's foreign ministry spokeswoman Hua Chunying said in a news briefing that she was unaware of details of the case. She said China consistently upholds the handling of such matters in accordance with domestic and international law and humanitarian principles.
The arrests come amid a crackdown by China on North Korean defectors. Chinese security services have apprehended at least 49 North Koreans in the three months between July and September, according to the charity Human Rights Watch - a significant jump from the 51 people recorded as having been detained over the entire previous 12 months.
At least nine of those arrested over the past three months are known to have been forcibly repatriated back to North Korea, according to Human Rights Watch.
"North Korean refugees and their families overseas deserve international support," said Phil Robertson, deputy Asia director for the charity, said in a statement.
"Governments around the world and the United Nations High Commissioner for Refugees should call on China to stop sending North Koreans back across the border to face torture, forced labour, sexual abuse, and worse," he said.
Lord Alton, who is chair of the UK's cross-party parliamentary group on North Korea, told the BBC he had urged the British government to intervene.
"Anyone who has read the United Nations' report on North Korea's crimes against humanity knows that these escapees face torture, imprisonment, forced labour or even execution," he said.