LUANDA, Angola — An ambitious reconstruction plan after Angola’s civil war was meant to reach even the country’s most faraway corner, a region known as the Land at the End of the World.

But the area’s new paved road abruptly turns to dirt about five miles before reaching the city of Cuito Cuanavale, the result of a mysterious disappearance in public funds.

“They’re building, but they’re not doing it well,” said Domingos Jeremias, 48, a farmer whose assessment was echoed by the other men milling around the center of the city, obliterated during the war, which lasted from 1975 to 2002. “There’s always something missing.”

When the war ended, Angola enjoyed a once-in-a-lifetime opportunity. Its production of oil was set to swell and prices would remain high for years. Unlike many other African nations emerging from war, Angola had more than enough money to rebuild, on its own terms, a landscape destroyed by conflict.

The skyline of the capital, Luanda, was quickly reshaped with skyscrapers. Gigantic satellite towns, the likes of which had never been seen in Africa, mushroomed in the outskirts of Luanda. New roads and railways stretched into the interior.

But Angola’s reconstruction and oil boom also presented the politically connected — those with “relatives in the kitchen,” as Angolans say — with a golden opportunity for self-enrichment. In an economy driven by President José Eduardo dos Santos, his inner circle of family and allies have amassed extraordinary wealth.

The president’s eldest daughter, Isabel dos Santos, has become Africa’s first female billionaire, according to Forbes Magazine, which estimates her wealth at $3.3 billion.

But as a drop in oil prices has stilled the cranes across Luanda’s skyline, and as Mr. dos Santos prepares to step down this year after 38 years in power, the country’s reconstruction, and the wealth of its ruling class, are coming under greater scrutiny and criticism — even from insiders.

Lopo do Nascimento, a former prime minister and onetime secretary general of the ruling party, said that spending on reconstruction had been “like opening a window and throwing out money.”

Billions spent on rebuilding — guided by politically connected Angolans and carried out by foreign contractors — vanished into individuals’ pockets, according to politicians, businessmen and academics. Little was done to ensure the money spent on reconstruction would yield lasting benefits to Angola’s economy.

“It’s now time to say, ‘If building or rebuilding this costs 10, I won’t invoice for 20 and pocket the other 10,’” Mr. Nascimento said in an interview at his home, a large villa with half a dozen luxury cars parked in an inner driveway.

It is impossible to determine exactly how much has disappeared from government coffers, though there are clues.

From 2002 to 2015, $28 billion from government budgets remain unaccounted for, according to the Catholic University of Angola’s Center for Studies and Scientific Research, which analyzes the government’s budgetary figures. Up to 35 percent of the money spent on road construction alone has vanished, according to a study by the center.

During the same period, Angolan companies and individuals invested $189 billion overseas in often opaque transactions, according to the center.

“Who are those people making investments outside the country?” asked Francisco Miguel Paulo, an economist at the center. “How did they earn that money?”

Improvements Amid Poverty

When peace finally came after 27 years of civil war and, before that, 13 years of a war of liberation against the country’s former colonial ruler, Portugal, much of the country lay in ruins.

Today, Angola has thousands of miles of new roads and railways, new airports, sports stadiums, hydroelectric dams, water treatment centers, government buildings and fancy shopping malls.

In Huambo, a city that was the rebellion’s headquarters and was destroyed during the war, few buildings still carry the war’s scars. In the city center, stately government buildings, including a provincial library, surround a large roundabout.

On a 500-mile drive from Huambo, in the country’s center, to Cuito Cuanavale, in the southeast, every small town appeared to have a new school or clinic — easily spotted because government buildings are painted pink.

“We’re satisfied,” said Jacob Candimba, 27, a resident of Cuito Cuanavale. “Before, we didn’t have roads, water or electricity.”

But in the capital, even though this is where the government has focused its reconstruction, there was still seething anger.

In Sambizanga, a Luanda slum where Mr. dos Santos was born 74 years ago, narrow, muddy roads crisscross a labyrinth of concrete houses and tin shacks.

One recent afternoon, two days after heavy rains, a handful of young men drank beer on a dry strip of road.

“We live bad, without any basic sanitation, without any electricity,” said Luquene Antonio, 24, an unemployed plumber wearing rain boots.

Nearby, two children played inside an abandoned refrigerator floating in murky water.

Oil Billions for Rebuilding

Since 2002, Angola has spent $120 billion on reconstruction, according to the Center for Studies and Scientific Research. At its peak, spending reached $15.8 billion in 2014.

In the years after the war, new offshore oil fields came online, doubling Angola’s daily production to nearly two million barrels a day and turning its economy into one of the world’s fastest-growing.

From 2002 to 2015, Angola’s exports totaled almost $600 billion, nearly all of it oil. During that period, oil revenue swelled government coffers with $315 billion, according to Catholic University.

Oil also gave the Angolan government a freedom rarely seen in Africa, allowing it to circumvent Western governments and international lenders — and decide exactly how and what to rebuild. With oil-backed loans negotiated with China, Angola outsourced the country’s reconstruction to state-owned Chinese companies and their subcontractors. Companies from other Portuguese-speaking nations, like Brazil and Portugal, also shared in the building boom.

But the Angolan model of oil-for-infrastructure came with serious drawbacks, experts said. The deals between Angola and its foreign partners lacked transparency and often resulted in projects of poor quality, either because of a lack of oversight or outright corruption.