Afghanistan construction workers.
An Afghan man works at a construction site on the outskirts of Kabul (Reuters).

Haji Khalil Zadran, an Afghan businessmen who has received more than $125m in donor-funded construction projects, is under investigation by US inspectors for allegedly channelling millions of dollars to the insurgency network Haqqani, leaked documents to the news agency Reuters have revealed.

Despite the allegations, he still has internationally funded contracts for reconstruction projects around the country. The director of Zadran's Haji Khalil Construction Company, Hayatullah Nawabi, said the company was lined up to receive an $11m contract to build an airport in the eastern city of Khost.

The terrorist Haqqani network is linked with al-Qaida and accused of carrying out deadly bombings on civilians, attacking international forces and the kidnap of New York Times reporter David Rohde. They are said to be one of the deadliest insurgent groups in Afghanistan.

John Sopko, chief of the US Special Inspector General for Afghan Reconstruction (Sigar), said: "It makes absolutely no sense that individuals and entities designated as supporting the insurgency could receive US contracts.

"If they get a contract not only do they get US taxpayer money, but they could gain access to US personnel and facilities, putting our troops at risk."

Zadran denied the allegations and said they were the result of mistaken identity.

He has been linked with the company Saadullah Khan and Brothers Engineering and Construction Company (SKB), which is believed to be one of the companies owned by Sirajuddin Haqqani, the effective leader of the insurgent group.

Together with SKB, Zadran won a $15m contract to build a road between the eastern Afghan towns of Gardez and Khost for the US Agency for International Development in 2011.

Endemic corruption throughout Afghanistan has meant that some profits from contracts are being channelled to insurgents. An official US memorandum estimated that SKB was passing $1m-2m to the Haqqani a month.

Foreign governments have poured billions of dollars into Afghanistan in an attempt to secure peace and stability. Donors have little control over what happens to cash once it is received by the Afghan government and have been unable to prevent firms linked with insurgent groups from winning lucrative contracts.

Sigar reported that Washington has spent more than $92bn on reconstruction efforts since 2002 - a record for the US.