The U.S. may have to spend $6 billion over the next year alone to train and maintain Afghan police forces, a Pentagon official told a Senate subcommittee Thursday.

A large part of that money likely will go through a contracting program that since 2005 has been criticized repeatedly in government reports for inefficiency and lack of oversight. In a recent audit, inspectors found that the program could not account for millions of dollars from past years.

The police training is crucial since U.S. troops, under current policy, will leave the country only when the Afghan government can provide security for its citizens.

“Training the police in Afghanistan is part of our military mission,” Sen. Claire McCaskill, D-Mo, said at the Senate homeland security subcommittee hearing. “It is as important as anything else we are doing in this nation right now.”

Sen. Ted Kaufman, D-Del., called the situation “catastrophic,” adding that after the U.S. has already spent more than $6 billion and is about to authorize more money, the Afghan police still face many of the same problems. Those include lack of leadership, low pay, corruption, insufficient training and a low retention rate.

The training program for Afghan police is run by Falls Church, Va.-based DynCorp International under a contract worth $1.27 billion. But witnesses at the subcommittee hearing said the contract lacks clear objectives and stringent assessment.