Corruption, weak armed forces and a huge budget gap -- a US watchdog overseeing rebuilding efforts in Afghanistan Wednesday released a list of seven "high-risk areas" leaving projects vulnerable to waste and fraud as troops withdraw.

"American taxpayer dollars and our strategic and humanitarian interests in Afghanistan are being placed at unnecessarily high levels of risk by widespread failure to track results, anticipate problems, and implement prudent countermeasures," the special inspector general for Afghanistan reconstruction (SIGAR) John Sopko said.

"And, unlike countries at peace, those problems can lead to lives lost and our national security objectives hindered or denied."

After some 13 years, the US-led NATO combat mission will officially end on December 31 although some troops will remain to train and support the Afghan army and police, who have taken on responsibility for suppressing worsening Islamist violence nationwide.

Sopko and the SIGAR team have warned consistently that as international troops withdraw it will be increasing hard to keep an eye on reconstruction projects without their protection.

SIGAR, set up by Congress in 2008 to monitor the billions of dollars spent in Afghanistan, has set out seven issues which pose a "high-risk" which Sopko said posed "a potent threat" to reconstruction efforts.

Here is the list:

CORRUPTION/RULE OF LAW: "Corruption is one of the most serious threats to the US-funded Afghanistan reconstruction effort," the watchdog says, highlighting that it has repeatedly raised this issue.

It questions whether the State Department has developed a proper strategy to battle graft and drawn up plans to protect US funds, as well as to tackling corruption within the Afghan government.

SUSTAINABILITY: The watchdog maintains that much of $104 billion spent by the US since the 2001 invasion to oust the Islamic Taliban militants risks being wasted "because the Afghans cannot sustain the investment without" continued donor support.

In 2013 the war-torn country's annual revenue was only $2 billion, while its expenditure was $5.4 billion. The IMF expects the funding gap to remain at about $7.7 billion through 2018.

Improving the energy sector for example is vital to the country's long-term economic progress, but the Afghans cannot afford to pay for much of the electric power infrastructure provided by the Americans.

Likewise, millions invested in the health sector could also go up in smoke because the Afghan government will not be able to afford to maintain and operate new hospitals.

THE CAPACITY OF THE AFGHAN SECURITY FORCES: Some $62 billion or, more than half of all the US expenditure, has gone towards building up the Afghan security forces. Military experts have warned this could be put at risk unless proper training and advise missions are left in place.

DIRECT FUNDING ASSISTANCE: Since 2010 the US and international donors have been replacing aid in the form of contracts and grants, to direct assistance into the Kabul government's coffers to give Afghans more freedom to manage their budget. SIGAR is increasingly concerned that many Afghan government agencies are ill-equipped to handle such a flow of money and has called for strong internal controls and greater oversight.

COUNTERNARCOTICS: "The expanding cultivation and trafficking of drugs puts the entire US and international investment in the reconstruction of Afghanistan at risk," the report says. Drug-trafficking feeds the Taliban and Al-Qaeda insurgency as well as corruption and organized crime.

CONTRACT MANAGEMENT: US agencies have failed to consistently manage civilian contractors, and no one knows precisely how much has been spent on them since 2002. The report also detailed a number of problematic projects under construction by local contractors.

STRATEGY AND PLANNING: A lack of implementation or operational planning "threatens to cause agencies and projects to work at counter-purposes, spend money on frivolous endeavors or fail to coordinate efforts."