Two US journalists were detained by the North Koreans on Tuesday while reporting from the China-North Korea border. The BBC's Michael Bristow was also on the border on Tuesday. Here he reports on what he found.
There are few signs of motorised transport along the river
The border between China and North Korea, which stretches for nearly 1,500km (900 miles), is heavily guarded by soldiers from both countries.
Two rivers, the Yalu and the Tumen, act as the border along much of its length. But wire fences have also been erected, sometimes on both sides.
The border seems to be more heavily guarded on the North Korean side. There are military points every few kilometres in some places.
Foreigners are not usually welcome in North Korea so it is difficult to get information about what is going on inside the country.
But it is possible to hire a boat and travel along the Yalu River to get a glimpse of ordinary life in the secretive socialist state.
The BBC took a boat along the river just outside the Chinese border city of Dandong, through which much of the cross-border trade passes.
Praise for leader
It is obvious from a brief look at North Korea that the country is very poor.
North Korean farmers working in the fields were using their hands. There were no tractors, not even horses.
There appears to be little mechanisation in this rural area. A cow-pulled cart was being loaded with water from the cool, clear river.
North Korea is happy to show off some aspects of its society
The BBC also spotted a ferry taking passengers from an island in the river to the mainland of North Korea.
It was making slow progress because it was being powered by a large oar pulled from side-to-side by two men standing at the back of the boat.
There was also a commune of about a dozen bungalows on the island.
They looked like the kind of homes you could find on the south coast of England, but there was also something you would not find in the UK - a slogan over a gateway leading into the commune praises North Korea's founder father Kim Il-sung.
The World Food Programme says that nearly nine million North Koreans will need foreign food aid this year.
This rural face is one that North Korea's current leader, Kim Jong-il, does not want the outside world to see.
But in Dandong, North Korea does allow outsiders to get a glimpse of a more pleasing aspect of the country.
It runs several restaurants in the city in which young, pretty North Korean women sing, dance and serve delicious food.
Wearing traditional costumes, the women perform nightly for both Chinese and North Korean guests.
Shopping in Dandong
The relationship between China and North Korea was forged in blood. China sent an army to help the North during the Korean War.
Hundreds of thousands of Chinese soldiers died in the fighting and there is a memorial to their sacrifice in the centre of Dandong.
It is typical communist architecture. There is a tall, square tower surrounded by four sculptures showing courageous soldiers.
But this relationship is also about trade. North Korea relies on China for much of its food, fuel and guns.
Traders who sell to North Koreans have shops in the streets around China's customs post in Dandong.
North Koreans buy all kinds of items in Dandong
One of these traders is Li Hongde, who runs a shop that sells everyday items such as cups, plates and pans.
The cheapest thing he sells is a glass, which costs just 2 yuan (30 US cents, 21 UK pence). The most expensive item is a rice cooker that costs 2,760 yuan ($404, £284).
"Business isn't very good at the moment because it's winter and the political situation isn't very stable," he said.
He said North Koreans prefer buying household items made in South Korea because they are reliable - and marked with Korean characters.
But before taking their purchases home, the North Koreans scrub off any markings that show where they were made.
There is an array of items on sale at other shops in the district, including electric keyboards, bicycles and hammers.
Many items are taken to North Korea via Dandong's Sino-Korean Friendship Bridge, the main crossing point between the two countries.
It stands next to the Broken Bridge, the previous crossing point that was built by the Japanese and destroyed by US bombers in the Korean War.
The Friendship Bridge is able to carry road and rail cargo, but there is not much traffic at the moment.
In the space of an hour, a van, a couple of trucks and a short train crossed over. It does not seem like business is booming.