North Korea's surprise decision to ease restrictions on international aid operations as it battles chronic hunger is a major breakthrough which bodes well for future international cooperation, aid workers say.
But aid groups have warned the secretive regime that they will halt a new aid programme if it reneges on promises to let them check the distribution of food.
Most donors say monitoring is vital to ensure aid is not diverted to North Korea's military or ruling party, which have been accused of human rights abuses.
Five aid agencies announced this week that they had signed an unprecedented deal with Pyongyang to oversee the distribution of food aid from the U.S. government - the first U.S. bilateral assistance in eight years.
"It has been made very clear to North Korea that if it's discovered that food is going where it's not supposed to be going this programme ... will not continue," said Joy Portella, spokeswoman for Mercy Corps, one of the agencies.
Up to 6 million people, about a quarter of the population, need help, according to the United Nations World Food Programme (WFP), which is also dramatically expanding its operations in the country.
For the first time, the agencies will be able to keep tabs on the progress of the food from its arrival in the country to its distribution in institutions including hospitals, nurseries and orphanages.
"This represents a sea-change," said Victor Hsu, country director for World Vision.
"The entire humanitarian community has been urging the North Korean authorities to cooperate in regard to monitoring and they have not done that until now so this is indeed a very happy surprise for the sake of the children ... "
World Vision and Mercy Corps, which were also involved in a food aid programme in the late 1990s, are among a very small handful of aid groups working in the country. Most don't operate there because of the heavy restrictions imposed by Pyongyang.
The agencies said the terms of the new deal were unprecedented.
For the first time, the authorities will give them a list of institutions and the number of people in each one that they can check deliveries against.
Aid workers will be based in the field. In the past the authorities confined them to Pyongyang.
The agencies will be allowed to carry out random checks with 24 hours' notice. In the past they had to give about a week's notice.
The country's food shortages have been caused by a combination of floods, the global food crisis, political wrangles with key aid donor South Korea and trade issues with China. Experts say the situation is similar to a decade ago when famine killed an estimated 1 million people.
Hsu said children were beginning to show the same signs of malnutrition that were visible in the late 1990s. "I've noticed since 2005 the children are beginning to look bad again like in the 1990s. They have discolouration and blemishes on their faces. They look very small and skinny," he said.
Of the 500,000 tonnes pledged by the United States, the agencies will organise distribution of 100,000 tonnes to the northwest of the country. The WFP will oversee the rest. The first shipment arrived on Sunday.
Hsu said North Korea was allowing aid workers into 165 of its 211 counties. The others are off limits for what Pyongyang says are national security reasons. No food aid will be delivered there.
"What we said is that if we have no access then it means there will be no food - we made that very clear," Hsu said.
The resumption of U.S. food aid comes just days after North Korea blew up a plutonium-producing nuclear plant and provided details of its nuclear programmes. Washington has strongly denied any link.
"There have been discussions about the aid for months," Portella said. "It's not the kind of agreement that you could slap together in a few weeks. These discussions were going on well before the North Koreans handed over any nuclear disclosure materials."
The aid agencies were hopeful that the easing of restrictions would lead to greater cooperation.
"North Korea functions according to precedent and therefore if some precedent has been set they rarely go back," Hsu said.
Portella said the authorities had rushed through visas for aid staff and allowed foreign experts to carry out an assessment of food needs in June, even letting aid workers talk to people in their homes.
"All this points to the fact that they want to make this work." Portella added. "So far we are encouraged."