KABUL, Afghanistan — Afghanistan could face economic collapse if international assistance is abruptly cut as foreign combat forces are withdrawn, the World Bank warned, stressing that the war-ravaged nation will need billions of dollars in aid for a decade or more.

The forecast by the World Bank, released late Tuesday, reflects broader concerns that Afghanistan will enter into a deep recession as the international community gradually reduces both the aid it provides the government and starts drawing down the 130,000 troops currently in the country. That troop withdrawal, which is slated to be completed by the end of 2014, has already begun with the transition of security responsibility from NATO to Afghan forces in seven areas earlier this year.

"The full assumption of Afghan responsibility for security by end-2014, the drawdown of most international military forces and the likely reduction in overall assistance will have a profound impact on Afghanistan's economic and political landscape, extending well beyond 2014," the World Bank said in a report.

The organization said Afghanistan this year received $15.7 billion in aid, representing more than 90 percent of its public spending.

"International experience and Afghanistan's history after the Soviet military withdrawal in 1989 demonstrate that violent fluctuations in aid, especially abrupt aid cutoffs, are extremely dangerous and destabilizing," the report said.

It said that the international community had to find ways to mitigate the impact and find a more sustainable way to deliver aid in the years to come. The government of President Hamid Karzai has pinned much of its hopes on massive copper deposits and other mineral wealth, but exploiting those resources, which Afghan officials predict will bring in about $3 trillion, will take years.

"The extremely high level of current annual aid is roughly the same amount as Afghanistan's Gross Domestic Product and cannot be sustained," the study said.

The World Bank estimated that Afghanistan's domestic revenues are expected to increase from 10 percent of GDP in 2011 to 17.5 percent by 2021. The rise, however, is dependent on the opening of some mining facilities, efficient tax collection and a security situation that does not deteriorate.

Weighing heavily on the country's fiscal position is spending on the Afghan National Security Forces — slated to increase to 352,000 personnel by the end of 2014 — and basic and civil services. Those expenses will have grown to twice the size of revenues and will result in a shortfall of about $7.8 billion annually, or about 25 percent of the country's GDP in 2021.

"To close this enormous fiscal gap, Afghanistan must rely on continuing international funding to pay for most security costs if the size of the force remains at currently agreed levels," the study said.

If foreign funding does not materialize, then the World Bank said the Afghan government would have to make "extremely difficult and possibly destabilizing trade-offs," such as shrinking the security force or cutting funds from civilian spending.

Although the United States has spent $444 billion in Afghanistan since it invaded the country in late 2001 after the Sept. 11 terrorist attacks, and plans to spend $101 billion in fiscal 2011, most of that money "does not reach Afghanistan because it primarily funds salaries of international soldiers, purchases of military hardware, and the like," the World Bank said.

The Pentagon has already decided to start reducing its expenses in Afghanistan and President Barack Obama has ordered the withdrawal of the first U.S. forces, with 10,000 leaving by the end of this year and 23,000 by next September.

Nonmilitary spending is also being cut by some governments and agencies. U.S. State Department and USAID assistance will be cut from $4.1 billion in 2010 to $2.5 billion in 2011.

Karzai is expected early next week to announce that government forces will start taking charge of security in all or parts of 17 of Afghanistan's 34 provinces.

The transition includes a wide swath of northern and western Afghanistan, but only a few spots in the more violent south and east. It is the second step in a transition that Karzai hopes will leave his army and police in control of the entire nation by the end of 2014.

A successful handover is key to NATO's plan to withdraw most of its combat forces from Afghanistan after more than a decade of fighting there. Training the 352,000-man Afghan army and police is a key part of that strategy and among the most costly. The United States alone already paid $22 billion in 2010 and 2011 to train and equip the Afghans.

The insurgency has been taking its toll on the Afghan security services.

The Afghan Defense Ministry announced that so far this month 65 of its soldiers had been killed in combat, compared 59 in October. It said that 107 insurgents had been killed in November and 284 in October.

According to an Associated Press tally, 512 international troops have been killed so far this year in Afghanistan. At least 382 of those killed were Americans.