The U.S. military expects that sustaining the Afghan army and police forces after the planned withdrawal of American combat forces in 2014 will cost about $4 billion a year and that most of that money will have to come from the United States and other outside donors, a senior military official told The Washington Post on Thursday.

The Afghan government can afford to pay only about 12 percent of the expected price tag, the official told the Post. The majority of the remaining costs would be borne by the U.S. government. U.S. officials also are counting on big contributions from NATO allies to fund the Afghan forces beyond 2014, the Post said.

The Obama administration plans to announce the enduring price tag for the Afghan troops at a NATO summit in May.

Read more about the enduring cost of maintaining security in Afghanistan from The Washington Post