The death toll among Afghanistan's security forces will no longer be sustainable unless urgent measures are taken to address recruiting and training issues, a top U.S. general has said.

"They are fighting hard, but their losses are not going to be sustainable unless we correct this problem," Lieutenant-General Kenneth McKenzie said on December 4 at a hearing before the Senate Armed Services Committee amid frustration among Congressmen over a lack of progress in the 17-year conflict in Afghanistan.

McKenzie, who has been nominated to lead the U.S. military's Central Command that oversees wars in the Middle East and Afghanistan, also warned against an abrupt withdrawal of American forces or change in strategy.

The Western-backed government in Kabul has struggled to counter attacks from the Taliban and other militant groups since the withdrawal of most NATO combat troops in 2014.

In October, Defense Secretary Jim Mattis said Afghan forces had more than 1,000 dead and wounded during August and September alone.

And Afghan President Ashraf Ghani last month said the death toll among Afghan security forces since 2015 was close to 29,000 -- a figure far higher than anything previously acknowledged.

If confirmed, McKenzie, a Marine officer who served two tours in Afghanistan, would replace the General Joseph Votel, who is retiring, as head of U.S. Central Command.

McKenzie said that Afghan forces are still unable to effectively withstand the Taliban fighters, who now number about 60,000 in Afghanistan.

“If we left precipitously right now I do not believe they would be able to successfully defend their country," he said.

Some 14,000 U.S. soldiers are currently serving in Afghanistan, mainly training and advising the Afghan security forces, and McKenzie couldn't say how much longer the United States will remain in the country.

"I do know that today it would be very difficult for [the Afghan security forces] to survive without our and our coalition partners' assistance," he said.

"The operational military situation is largely stalemated," said the U.S. general, who also voiced optimism over invigorated U.S. efforts to settle the Afghan conflict.

U.S. special envoy Zalmay Khalilzad met on December 4 with Pakistani officials in Islamabad, and a Taliban official said four members from the group's political office in Qatar were also in Pakistan’s capital, according to the Associated Press news agency.

President Ghani on November 28 laid out what he called a "road map" for peace talks with the Taliban and said his government had formed a 12-person team for the negotiations.

The militants have long refused U.S. demands to directly negotiate with the Kabul government.

With reporting by AP, Reuters, and AFP