KUALA LUMPUR - United States President Donald Trump should press Pyongyang to end state-imposed slavery and forced labor, said North Korean defectors ahead of a historic summit between the leaders of both countries.With an estimated 1.1 million people - or one in 20 citizens - living in slavery, North Korea was ranked the worst country in the world in terms of prevalence in the 2016 Global Slavery Index by the rights group Walk Free Foundation.Trump and North Korean leader Kim Jong Un are due on Tuesday for the first ever face-to-face meeting by leaders of the two nations, with the focus on Pyongyang's nuclear weapons and peace on the Korean Peninsula.Defectors and campaigners said the summit in Singapore should highlight human rights abuses."It is not time to focus on nuclear weapons. It is time to focus on how North Korea oppresses its people," Yeonmi Park, a defector, told the Thomson Reuters Foundation by phone from New York, where she now lives.Yeonmi was raped and fell into the hands of traffickers after she crossed into China in 2007 at age 13. She campaigns against the trafficking of North Korean brides into China, and recounted her ordeal in the 2015 memoir In Order to Live.Many North Koreans are trapped in prison camps inside the country, or sent abroad as slave laborers to earn much-needed income for the isolated state.The United Nations said in 2015 that North Korea had forced 50,000 people to work abroad, mainly in Russia and China, earning between $1.2 billion to $2.3 billion annually for the government.The European Alliance for Human Rights in North Korea said that Pyongyang was using these "state-sponsored slaves" to generate income by circumventing international sanctions over its nuclear weapons programme.The laborers commonly work shifts of 10 to 12 hours, and up to 90 percent of their pay is sent back to North Korea, according to the group."If [Trump and Kim] don't talk about the human rights issues, I am worried there could be many more who die of torture in the future," said Jihyun Park, a defector who now lives in Manchester, in northwest England.The 49-year-old, who is not related to Yeonmi, was sold to China as a bride, but was later arrested and deported back to North Korea. She was sent to a prison camp, where she and others worked barefoot, farming mountainous terrain from dawn to dusk."Many people still don't know the situation inside North Korea," said Jihyun, an outreach director with Connect North Korea, a group that supports refugees who have escaped the country and are now living in Britain.