A former US envoy to NATO, Douglas Lute, told ABC the United States is stuck in a political and military stalemate in Afghanistan, and it is unclear whether President Donald Trump's new strategy in the country will resolve it.

"If our goal is stalemate, we've achieved it," Lute told ABC News Chief Anchor George Stephanopoulos in an interview on "This Week" Sunday that also included Zalmay Khalilzad, who served as US ambassador to Afghanistan and the United Nations under President George W. Bush.

Lute was responding to Trump’s announcement last week about his new war strategy in Afghanistan.

"We have not only a stalemate on the security situation, but a threefold stalemate on the political front," said Lute, who served as an adviser on Afghan policy under both former presidents George Bush and Barack Obama.

"We have a political stalemate in Kabul. We have a political stalemate in the region, and we have a political stalemate with regards to trying to enter talks between the Afghan government and the Taliban," said Lute.

But Khalilzad took a different view, telling Stephanopoulos that he believes the stalemate "has been shifting in favor of the Taliban in recent weeks and months."

"They have been gaining ground," he said.

"So why should they negotiate for peace if they think they're going to win the war?"

However, Khalilzad pointed out an important change in Trump's new strategy is its "sharp focus" on Pakistan.

"This has been in my judgment the single most important factor, the Pakistan problem, for prolonging the war," Khalilzad said.

"We have the leverage of cutting off assistance," he said. "We have the leverage of putting ... individuals who support groups such as the Taliban on a blacklist."

But Lute disagreed. "I'm actually skeptical that we have sufficient leverage against Pakistan to change their strategic calculus," he said.

ABC reported however that both Lute and Khalilzad agreed more details are needed to fully assess Trump's Afghanistan strategy.

"We heard a lot about what it is we want to accomplish," Lute said. "We heard very little on how."