The United Nations says the world is facing its biggest humanitarian crisis since the end of World War Two. A famine has already been declared in parts of South Sudan. There have also been warnings of possible famine in north-east Nigeria, Somalia and Yemen. The UN says in all nearly 20 million people are at risk of starvation. Why are there still famines and what can be done about it?
What is happening in South Sudan?
UN agencies say 100,000 people are facing starvation in South Sudan and a further 1 million there are classified as being on the brink of famine. This is the most acute of the present food emergencies. It is also the most widespread nationally. Overall, says the UN, 4.9 million people - or 40% of South Sudan's population - are "in need of urgent food, agriculture and nutrition assistance".
"Many families have exhausted every means they have to survive," says the UN's Food and Agriculture Organization representative in South Sudan, Serge Tissot.
The main cause of the famine is conflict. The country has now been at war since 2013 and more than 3 million people have been forced to flee their homes.
As World Food Programme country director Joyce Luma says: "This famine is man-made."
"The people are predominantly farmers and war has disrupted agriculture. They've lost their livestock, even their farming tools. For months there has been a total reliance on whatever plants they can find and fish they can catch," says Mr Tissot.
Crop production has been severely curtailed by the conflict, even in previously stable and fertile areas, as a long-running dispute among political leaders has escalated into a violent competition for power and resources among different ethnic groups.
As crop production has fallen and livestock have died, so inflation has soared (by up to 800% year-on-year, says the UN) causing massive price rises for basic foodstuffs.
This economic collapse would not have happened without war.
What does the declaration of famine mean?
The UN considers famine a technical term, to be used sparingly. The formal famine declaration in South Sudan means people there have already started dying of hunger.
More specifically, famine can be declared only when certain measures of mortality, malnutrition and hunger are met. These are:
- at least 20% of households in an area face extreme food shortages with a limited ability to cope;
- acute malnutrition rates exceed 30%;
- and the death rate exceeds two persons per day per 10,000 persons.
Other factors that may be considered include large-scale displacement, widespread destitution, disease outbreaks and social collapse.
The declaration of a famine carries no binding obligations on the UN or anyone else, but does bring global attention to the problem.
Previous famines include southern Somalia in 2011, southern Sudan in 2008, Gode in the Somali region of Ethiopia in 2000, North Korea (1996), Somalia (1991-1992) and Ethiopia (1984-1985).
The possibility of three further famine declarations in Nigeria, Somali and Yemen would be an unprecedented situation in modern times.
"We have never seen that before, and with all of these crises they are protracted situations and they require significant financing," World Food Programme director of emergencies Denise Brown told the Guardian. "The international community has got to find a way of stepping up to manage this situation until political solutions are found."
How much aid is needed?
UN humanitarian chief Stephen O'Brien said that more than 20 million people faced the threat of starvation and famine in north-east Nigeria, Somalia, South Sudan and Yemen.
Unicef has already warned 1.4 million children could starve to death this year.
Mr O'Brien said $4.4bn (£3.6bn) was needed by July to avert disaster.
"We stand at a critical point in history," Mr O'Brien told the Security Council last week. "Already at the beginning of the year we are facing the largest humanitarian crisis since the creation of the United Nations."
What can be done in South Sudan?
In the immediate term, two things would be necessary to halt and reverse the famine: More humanitarian assistance and unimpeded access for humanitarian agencies to those worst affected.
UN agencies speak of handing out millions of emergency livelihood kits, intended to help people fish or grow vegetables. There has also been a programme to vaccinate sheep and goats in an attempt to stem further livestock losses.
But, says Ms Luma, "we have also warned that there is only so much that humanitarian assistance can achieve in the absence of meaningful peace and security".
The areas where a famine has been declared are in parts of Unity State seen as sympathetic to the rebels.
Although it denies the charges, President Kiir has promised "that all humanitarian and development organisations have unimpeded access to needy populations across the country".
But apart from that, there has been no indication that the huge suffering of civilians will prompt South Sudan's warring parties to stop fighting.
Why are there food crises elsewhere?
The common theme is conflict.
Like South Sudan, Somalia and Yemen are all fairly poor countries where fighting has severely disrupted stability and normal life, pushing people over the edge. The same is true for north-east Nigeria.
People are so busy trying to survive that they are unable to earn a living by going to work, farming or looking after their animals.
In Somalia, a drought has killed many animals which are the main source of income for millions of nomads.
What is happening in Nigeria?
The north-east of the country has been badly hit by an eight-year insurgency by Islamist militant group Boko Haram.
Although the army has now pushed it out of most of the areas it had seized, some 2.4 million people have fled their homes and are unable to farm their land.
Although Nigeria is a major oil exporter, many people live in poverty at the best of times, especially in the arid north.
What about Somalia?
Somalia was the last country to experience a famine, in 2011.
It has been without a functioning national government for more than 25 years and has been wracked by constant conflict during that time.
Islamist militant group al-Shabab still controls many rural parts of the country.
While al-Shabab does allow normal economic life such as farming and livestock herding to carry on, Western aid agencies are not able to operate in these areas.
The conflict between the African Union-backed government in Mogadishu and al-Shabab has exacerbated the situation.
A severe drought has affected the entire Horn of Africa.
Ethiopia and Kenya have also been badly hit by the lack of security and the inability of aid workers to reach many parts of the country mean Somalia has been feeling it worst.
What is happening in Yemen?
In Yemen, a multi-party civil conflict has drawn in regional powers, causing widespread destruction, economic damage and loss of life.
Yemen has long-standing water shortages and successive governments have been criticised for not doing more to conserve resources and improve the country's ability to feed itself.
Even before the conflict started, nearly 90% of Yemen's food had to be imported, Oxfam says.
It is estimated that 18.8 million people, or 69% of Yemen's population, need of some form of humanitarian assistance. That includes 10.3 million in acute need, who urgently require immediate, life-saving assistance in at least one sector.
Yemen usually imports more than 90% of staple food. But a naval embargo imposed by the Saudi-led coalition, fighting around the government-controlled port of Aden and air strikes on the rebel-held port of Hudaydah, have severely reduced imports since 2015.
A lack of fuel, coupled with insecurity and damage to markets and roads, have also prevented supplies from being distributed.
How is it different for more stable countries?
In Kenya, the government has declared a national disaster because of the drought in parts of the country and announced a compensation scheme for those who have lost livestock.
The Kenya Red Cross has been making cash payments, distributing food vouchers and aid and helping livestock owners sell off weakening animals before they die.
This kind of ameliorative action is much less possible or likely in countries affected by war.
UN assistant secretary general Justin Forsyth told the BBC: "Nobody should be dying of starvation in 2017. There is enough food in the world, we have enough capability in terms of the humanitarian community.
"In South Sudan, Unicef has 620 feeding centres for severely malnourished children, so the places where children are dying are places we can't get to, or get to only occasionally. If there was access, we could save all of these children's lives."
The US-based Africa Center for Strategic Studies says 19 African countries are facing crisis, emergency, or catastrophic levels of food insecurity.
Of these, 10 are experiencing civil conflict. Eight of these are autocracies and the source of 82% of the 18.5 million Africans who are internally displaced or refugees, the ACSS says.