WASHINGTON (REUTERS) - The United States (US) government should reconsider whether to spend more on reconstruction aid in Afghanistan, the US watchdog who monitors the funds said on Wednesday, citing Afghanistan's persistent corruption and inability to manage projects as US troops withdraw.

Mr John Sopko, the special inspector general for Afghan reconstruction, said US$20 billion (S$25 billion) in US assistance for Afghanistan had been appropriated but not yet spent. Nearly US$10 billion more in aid may soon be approved by Congress.

Mr Sopko asked whether any of this money should be released. A growing number of projects built with US assistance in Afghanistan are now in insecure areas as US troops withdraw, putting them beyond the reach of American auditors to safely visit, he said.

"We have the opportunity to hit the pause button" as US troops are pulling out, Sopko told a House of Representatives committee. "It's an important opportunity to stop and reassess all of that money that hasn't been spent, and make the determination, is it worth the risk?"

"There may be a reason to push the money out the door for a particular project or program... But at least justify it," he said, speaking to the national security subcommittee of the House Oversight and Government Reform panel.

Mr Sopko's remarks came amid growing questions over US spending on Afghanistan.

The subcommittee chairman, Republican Representative Jason Chaffetz, said it was especially distasteful for Washington to be sending taxpayers' money to "the most corrupt government on the face of the planet" in a time of fiscal scarcity at home.

Afghanistan is regularly ranked as one of the world's most corrupt countries. The inspector general's audits have pointed out numerous weaknesses in the oversight of US reconstruction aid to Afghanistan, which is approaching a US$100 billion over a decade of war. Much of this money has gone to help train Afghan military forces.

President Barack Obama said on Tuesday he would withdraw 34,000 troops - about half the US forces in Afghanistan - by the end of this year.

That would be followed by further troop withdrawals next year to wrap up the war there, Mr Obama said in his State of the Union speech.

Mr Sopko, who has been in his job for seven months, said his office will write letters to all US agencies operating in Afghanistan asking them to list the status of projects there.

Congress and the administration should examine the list and decide whether to forge ahead with the projects that have not begun, he said.

For example, he said, "If the Afghans can't sustain a hospital, why build it?" Mr Sopko is auditing some hospitals and clinics that were built in Afghanistan with US help.

Mr Chaffetz of Utah and the panel's top Democrat, Mr John Tierney of Massachusetts, have introduced legislation to prevent the United States from buying more fuel for the Afghan Army without stricter accounting measures.

A recent audit by Mr Sopko's office showed that for more than US$1 billion of fuel Washington bought for the Afghan military, records for US$201 million in purchases were missing.

That increased the risk that funds and fuel were lost or stolen, or that purchases were made from Iran in violation of US sanctions, the audit said.