The revelation is so disturbing that it might once have shocked the world into action: the mounting evidence that an oil-rich regime is using the brutal tactic of deliberate starvation to crush a revolt by its own citizens.

Yet as famine and death spread in the world's newest country, there is little sign of any urgent response by the world's most powerful leaders. Instead there are growing fears that political apathy and U.S. budget cuts will make the catastrophe even worse.

The man-made disaster is unfolding with relentless momentum in South Sudan, where three years of civil war have brought famine and forced nearly two-thirds of its 11 million people to depend on humanitarian aid. At least 79 aid workers have been killed since the war began, including six killed on Saturday in an ambush in government-controlled territory.

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The famine, declared last month, is the first anywhere in the world in nearly six years. South Sudan is now one of four countries where 20 million people are on the brink of famine – one of the world's worst humanitarian crises since the Second World War.

Less than six years ago, the United States and Canada were among the many nations celebrating South Sudan's hard-fought independence from the Sudanese dictatorship. With its oil wealth and strong Western support, South Sudan seemed to have a bright future.

Instead it has collapsed into deadly anarchy, with repeated warnings that it could be on the verge of genocide. Tens of thousands of civilians have died. Half of the government's budget is reportedly being spent on weapons and soldiers for the war. And now the government is using its chokehold on relief supply routes to starve its opponents and control the impoverished population.

United Nations officials have reported that South Sudanese soldiers are blocking the roads into regions where aid is desperately needed, demanding money and forcing dozens of relief convoys to turn back, and sometimes even attacking the convoys. In effect, the regime is using food blockades as a weapon of war, at a time when 100,000 people are officially in famine and another million are on the brink of famine.

Because so many roads are blocked or dangerous, the UN has been forced to drop its food aid from airplanes flying above the malnourished regions, at a far higher cost than land routes.

A leaked UN report has concluded that the famine in South Sudan is largely due to the "cumulative toll" of government military operations and restrictions on relief operations. The famine, unsurprisingly, is in an opposition-controlled region.

To make the crisis even worse, the government is creating new obstacles for relief agencies, demanding an extortionate fee of $10,000 (U.S.) for every work permit for a foreign aid worker. (The fee was previously $100.)

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"The government's continued unconscionable impediments to humanitarians … may amount to deliberate starvation tactics," said Michele Sison, the U.S. deputy representative to the United Nations, at a Security Council meeting last Thursday.

She said the government was using a "scorched earth campaign" to destroy thousands of homes. "The famine is not a result of drought," she said. "It is the result of leaders more interested in political power and personal gain than in stopping violence and allowing humanitarian access."

At the same Security Council meeting, UN Secretary-General Antonio Guterres said the government is refusing even to acknowledge the existence of the crisis. "The government continues to impede deliveries of life-saving assistance, including through access denials and bureaucratic impediments," he told the council. "The government has yet to express any meaningful concern or take any tangible steps to address the plight of its people."

The disaster is so devastating that South Sudan has become the world's fastest-growing refugee crisis, with 1.6 million of its people fleeing across borders into Uganda and other countries.

The UN is seeking $4.4-billion by the end of March to prevent a catastrophe in South Sudan and three other famine-threatened countries: Yemen, Somalia and Nigeria. Yet by February, only 2 per cent of this target had been raised.

The Canadian government this month announced $119.25-million (Canadian) in humanitarian aid for the four famine-threatened countries, and other countries are beginning to chip in. But the UN's food agency, the World Food Programme, has been so underfinanced for years that it has had to cut rations to refugees and other recipients.

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At the same time, U.S. President Donald Trump is proposing sharp cuts to foreign aid, including UN agencies. The United States is traditionally the biggest donor to UN relief operations, so the cuts could have a far-reaching effect. The cuts wouldn't take effect until next year, even if they are confirmed by Congress, but they are sparking fears that the South Sudan crisis could accelerate in the longer term, with less global support.

Despite the mounting outrage over the widening famine and the deliberate blocking of relief operations, the UN Security Council has failed to come up with any fresh tactics to solve the crisis. Several of its members, including the United States and Britain, have talked of international sanctions and an arms embargo to put pressure on the government. But when the United States pushed for an arms embargo against South Sudan last December, eight of the 15 council members abstained and the proposal failed.

The UN is also pushing for a Regional Protection Force to provide greater security in the country, but the South Sudan government has thrown up obstacles to delay it.

As frustration grows, an increasing number of independent analysts and think tanks are suggesting a more radical alternative: removing the entire government and putting South Sudan under an international trusteeship.