Tokyo - Sanctions aimed at punishing the North Korean regime are hampering the ability of aid groups to operate inside the country, triggering warnings that the international campaign is harming ordinary North Koreans.
Difficulties in obtaining supplies, including medical equipment, and in transferring money to fund aid programs could have a direct impact on health and nutrition levels throughout North Korea, they say.
"We need to deal with the nuclear problemme, but we need to properly ponder our means for achieving that goal," Tomás Ojea Quintana, the U.N.'s special rapporteur on North Korean human rights, said in an interview in Tokyo.
About 70 percent of the North Korean population is already categorised as "food insecure," meaning constantly struggling against hunger, and one in four children's growth is stunted.
The sanctions could increase the levels of food insecurity and the incidence of acute malnutrition among children.
"These are not just statistics. This is reality in the DPRK," Quintana said, using the abbreviation for North Korea's official name.
"It's my responsibility to remind the Security Council that they should develop a comprehensive assessment of the possible impact of their sanctions. What is the concrete impact on humanitarian agencies working inside North Korea?"
The U.N.'s World Food Program, UNICEF, the World Health Organisation and the U.N. Development Program all have operations in North Korea. A small number of American and other humanitarian agencies provide food, medical and agricultural assistance from bases outside the country.
But the waves of multilateral and direct American sanctions that have been imposed on Kim Jong Un's regime following its missile launches and nuclear tests have now made operations so difficult that some agencies are pulling out. Save the Children has shut down its operations in Pyongyang, billing the move as a "temporary suspension."
"US and international humanitarian NGOs working in North Korea are experiencing death by a thousand cuts," said Keith Luse, executive director of the Washington-based National Committee on North Korea, which includes many humanitarian agencies among its members.
"These sanctions were not intended for them, but they have ended up being victims of the international sanctions regime," Luse said.
The difficulties have mounted as the crackdown has broadened from "smart sanctions" designed to cut off parts and funding for the nuclear weapons program to more general measures that are starting to look like a trade embargo.
President Donald Trump has vowed to use "maximum pressure" to persuade North Korea to give up its nuclear weapons program.
Sanctions imposed in September through the U.N. Security Council, at the United States' instigation, banned North Korean exports of seafood, garments and coal, adding to previous prohibitions on commodities.
Japan, which holds the rotating presidency of the Security Council, is urging other member states to cut off humanitarian aid to North Korea.
The campaign is having a tangible impact.
The U.K. government announced that it would no longer send assistance to North Korea. "We will use whatever means we have to make clear our displeasure at the reckless provocations from Kim Jong Un," Mark Field, the British minister of state for Asia, told South Korea's Yonhap News Agency in Seoul last month.
The South Korean government, which has vowed not to let political considerations affect humanitarian decisions, has not delivered on its September pledge to give $8 million to the World Food Program and UNICEF for children and pregnant women.
Seoul was still "in consultation" with the two agencies, said unification ministry spokesperson Choi Ji-Seon.
For the relatively few aid agencies still working to help North Koreans, they face increasing bureaucratic challenges to operate in a country already replete with difficulties.
The sanctions were becoming a "serious concern" for U.N. agencies operating in North Korea and could "hamper assistance and relief activities," Tapan Mishra, the U.N. resident coordinator in Pyongyang, wrote in letters to U.N. officials at the end of October.
"Crucial relief items, including medical equipment and drugs, have been held up for months despite being equipped with the required paperwork affirming that they are not on the list of sanctions items," he wrote in the letters, which were first reported by NK News, a specialist site.
Items that had been blocked included anesthesia machines used for emergency operations and digital X-ray machines needed to diagnose tuberculosis.
American aid agencies must get licenses from the Commerce or Treasury departments to send goods needed for their work into North Korea and now are required to get special dispensation to airfreight time-sensitive equipment, such as medical supplies, because Air Koryo, North Korea's national carrier, was sanctioned.
"It's all very tricky and new for us," said one American humanitarian worker, who spoke on the condition of anonymity because sensitive negotiations were ongoing. "It's been weeks and months of back and forth and talking to lawyers. It's very complex and challenging, but if we don't do it, we can't continue."
Chinese customs officials are also cracking down on shipments to North Korea - and to a surprising extent given Beijing's previous halfhearted implementation of international sanctions.
They have become stricter about shipments, asking for detailed inventories, including lists of manufacturers' names and materials used in every item. A container of wheelchairs sent by a South Korean aid agency was blocked by China, as were water purification tablets meant for flood victims, according to people with knowledge of the incidents.
A Pyongyang-based humanitarian worker said there were also "self-imposed sanctions" by suppliers in China.
"Chinese suppliers who had been sending us raw materials we need for our projects have just suddenly disappeared," the worker said, speaking on the condition of anonymity so as not to jeopardise the humanitarian work. "They're not doing anything that's banned by sanctions, but they seem to have decided that it's not worth the exposure or the risk to their reputations."
Meanwhile, Chinese banks are refusing to handle any money related to North Korea, say humanitarian workers who are trying to wire money to Chinese suppliers of medical equipment for use inside North Korea - even when the supplier is Chinese-owned.
While foreign journalists invited to North Korea see the impressive construction projects in the capital, life is very different in the rest of the country, say regular visitors.
"It's going to be the people who are the most vulnerable, the people outside Pyongyang, who will suffer," said Kee Park, an American neurosurgeon who performs operations in North Korea.
The sanctions on the fishing, garment and coal industries, coupled with South Korea's decision to close a joint factory complex that employed more than 50 000 North Koreans, will deprive many people of their incomes in an economy that is increasingly market-based, Park said.
"Sanctions are designed to hurt so that the government will change its policy," he said. "But they're hurting the wrong people."