A U.S. government watchdog says a lack of coordinated oversight of U.S. spending in Afghanistan has led to a waste of funds and hampered the training and development of Afghan security forces.

The Special Inspector General for Afghanistan Reconstruction (SIGAR) said in a report to Congress late on June 20 that the United States spent nearly $84 billion on Afghan forces. But SIGAR said Afghan forces continue to suffer heavy casualties, high levels of desertion, and face problems with organization and logistics.

"Security-sector assistance efforts in Afghanistan have been hindered by the lack of clear command-and-control relationships between the U.S. military and the U.S. Embassy, as well as between ministerial and tactical advising efforts," the report said.

"This has resulted in disjointed efforts to develop" the capabilities of Afghan forces' capabilities, it said.

The report also said that, from the start, the "security-sector assistance mission in Afghanistan lacked an enduring and comprehensive plan." from the start.

Afghan security forces have struggled to fend off the Taliban insurgency since NATO's combat mission ended in December 2014.

The United States has about 14,000 troops in Afghanistan. Most are serving in the NATO-led Resolute Support mission to train and advise Afghan government forces. Some U.S. troops are taking part in separate combat operations against the Taliban and other militants.

At the same time, the United States has intensified its efforts to negotiate an end to its nearly 18-year war in Afghanistan.

Zalmay Khalilzad, the U.S. envoy seeking a peace deal with the Taliban, has held several rounds of talks in Qatar with senior members of the militant group.

The sides have made progress. But the Taliban has so far rejected direct negotiations with the Western-backed Afghan government.