Ringed with snipers and sandbag bunkers, the makeshift office of a Kabul academic spearheading President Ashraf Ghani's unprecedented anti-corruption drive could be mistaken for a military garrison.

Handpicked by Ghani to oversee his anti-graft campaign is Hamidullah Farooqi, a Kabul University economics lecturer who was part of the president's election campaign.

"I used to live an ordinary life driving an ordinary Toyota," said Farooqi, 62, reading glasses perched on his forehead. "But investigating corruption means investigating people with dangerous connections. It's like fighting the mafia - the economic mafia."

Corruption in Afghanistan is not just another issue. It is arguably the single biggest challenge confronting the troubled country as it rebuilds itself after decades of war.

It permeates nearly every public institution, hobbling development despite hundreds of billions of dollars of foreign aid over the past decade, sapping already bare state coffers and fueling insecurity as alienated Afghans veer toward the Taliban.

Since coming to power in September, Ghani, an American-educated former World Bank official, appears to be cracking down hard.

He launched a probe into 12 military logistics contracts, reopened the investigation into a major banking scandal and sacked nearly the entire administration of western Herat province accused of corruption or incompetence.

The most high-profile among these cases are contracts to supply fuel to the Afghan military worth nearly $1 billion, approved by the previous Hamid Karzai-led government.

Farooqi said the contracts, which Ghani terminated, involved "sophisticated" white-collar fraud.

Last week, Farooqi discovered one eye-popping detail that helped uncover the graft: four companies vying for the contracts submitted the exact same bidding prices - the numbers matched right up to the last decimal place.

"That's only possible ... if there is bidder collusion or if the price list is leaked (from inside the government)," he said.