WASHINGTON — A day after Defense Secretary Jim Mattis on Monday called for the international community to help end the war in Afghanistan, the incoming head of U.S. Central Command reluctantly acknowledged to lawmakers on Tuesday that he has no idea when U.S. troops may fully withdraw from Afghanistan.

But he insisted the 17-year conflict remains critical to national security, and that the price in both dollars and American lives is still justified.

“What we are doing is preventing the homeland from being attacked,” said Lt. Gen. Kenneth McKenzie Jr., the nominee to lead CENTCOM, in a hearing before the Senate Armed Services Committee. “That’s the clear, tangible effort we can honor (fallen troops) for.”

His comments come on the heels of increased questioning from civilian leaders about the ongoing mission overseas, which topped $45 billion in costs and claimed 14 American lives this year alone. That comes despite coalition forces officially ending combat operations in the country four years ago, and transitioning to a training role.

Lawmakers on the committee noted that despite the work, the Afghan government has actually lost territory in recent years, as Taliban and other insurgent forces reassert themselves in less populated areas.

And McKenzie said that those security forces are still heavily dependent on coalition support for the combat missions they are conducting throughout the country.

“They’re not there yet,” he said. “If we left precipitously right now, they would not be able to successfully defend their country.

“We’re going to go through this winter, we’ll see how they do. But I don’t know how long it’s going to take.”

That answer frustrated several members of the panel.

“We’ve been at it for 17 years,” said Sen. Gary Peters, D-Mich. “Seventeen years is a long time. What are we doing differently with the Afghan security forces that we haven’t done for 17 years?”

McKenzie insisted there have been important, positive changes.

“We are doing things significantly different. They are doing the fighting … they are doing it imperfectly, but they are doing it without assistance. That is a new thing.”

“And we have been pursuing a diplomatic solution for years, but not the way we are now. Not with an empowered envoy who is talking directly with the Taliban, where we have an opportunity to bring them together. I believe this is a new opportunity for us.”

McKenzie’s comments come just days after similar support for the mission from President Donald Trump and Defense Secretary Jim Mattis.

At the Reagan Defense Forum in California on Saturday, Mattis said he sees signs of progress in the fight, even as attacks against U.S. forces and civilian targets mount there.

“The Taliban have made clear the lives of the Afghan people are of no value to them,” he said. “They can’t win at the ballot box, so they are trying to terrorize instead.”

But on Monday, at an event with Indian military officials, Mattis told reporters that after 40 years of conflict in the region, “40 years is enough and it’s time for everyone to get on board, support the United Nations, and support … all those who are trying to maintain peace and make for a better world here.”

About 16,000 U.S. troops are currently deployed in Afghanistan in training and counterterrorism roles. More than 2,400 U.S. military personnel have died since the initial invasion of American forces in 2001.

McKenzie — who has deployed to Afghanistan twice in his career and seen his son serve two tours there as well — is expected to be confirmed to take over leadership of the combatant command by the end of the year.