Afghanistan may be the "graveyard of empires," but the U.S. has no imperial ambitions there, Defense Secretary Jim Mattis told lawmakers Tuesday.

Mattis defended the U.S. strategy designed to break the will of the Taliban, under questioning from Rep. Walter Jones, R-N.C., at a House Armed Services Committee hearing. Jones invoked the famous “graveyard of empires” quote.

The North Carolina lawmaker, whose district includes Camp Lejeune, cited recent news headlines suggesting the Taliban is threatening 70 percent of Afghanistan. He also cited complaints from an internal Pentagon watchdog that the U.S. military was withholding information that would help the American public understand if President Trump’s new strategy was working.

Jones asked Mattis if he agreed with the assessment of retired Marine Corps Commandant Gen. Chuck Krulak, who wrote Jones in an email, “No one has ever conquered Afghanistan and many have tried. We would join the list of nations that have tried and failed."

“Congressman, if we were engaged in conquering Afghanistan, I would agree 100 percent with what you just stated, if that was our sense of empire,” Mattis said. “What we are doing to earn the trust of the American people is to ensure another 9/11 hatched out of there does not happen during our watch.”

Mattis acknowledged that after 16 years, the war in Afghanistan has been dragging on without notable progress.

“It's been a long, hard slog, and I recognize that,” he said, adding that among the skeptics he had to convince to try a much more robust support of the Afghans was the president himself, who was initially reluctant to sign off on the strategy.

“President Trump challenged every assumption. It took months to put it together to answer every question he had. And the gravity of protecting the American people caused him to change his mind,” Mattis said.

Mattis said the new strategy is a departure from all previous efforts because the Afghan forces are doing the fighting, and the U.S. is providing much more support in the form of airstrikes and fire support.

The top U.S. commander in Afghanistan, Gen. John Nicholson, announced Tuesday that the U.S. air campaign to take out Taliban training camps and drug labs had moved into northern Afghanistan over the past four days.

"The Taliban have nowhere to hide," Nicholson in a statement. "There will be no safe haven for any terrorist group bent on bringing harm and destruction to this country."

Mattis also said the order by the U.S. military to withhold some previously public information about the number of districts controlled in Afghanistan by the Afghan government as compared to the Taliban was a mistake.

“I would also tell you that any attempt to keep information from the American people — it was a NATO decision at that point. It was a mistake,” Mattis said. “I might add that information is now available.”

In his latest report to Congress last month, Special Inspector General for Afghanistan Reconstruction John Sopko said he was told not to release the information, which he called “one of the last remaining publicly available indicators for members of Congress and for the American public of how the 16-year-long U.S. effort to secure Afghanistan is faring.”

The next day, a spokesman for the NATO-led Operation Resolute Support said a human error was to blame for the inadvertent classification of the data.

“The classification system, because it incorporates both a NATO and U.S. nomenclature, can be challenging, and a mistake was made,” said Navy Capt. Tom Gresback, public affairs director for the NATO-led mission. “The data is not classified, and there was no intent to withhold it unnecessarily.”

At a separate hearing before the Senate Foreign Relations Committee, a State Department official testified that despite recent Taliban and Islamic State attacks that killed and wounded hundreds of Afghans, the president's strategy is showing some signs of progress.

“On the battlefield, we're seeing the Taliban's momentum begin to slow. No major population center has fallen to the Taliban since its temporary occupation of Kunduz City in 2015,” said John Sullivan, deputy secretary of state.

“Afghan forces are now on the offensive. Our allies and NATO partners, contributing more than 6,500 troops, are actively supporting our vision for a stable Afghanistan ... and in the Afghan government, we have a partner that is tackling economic, political, security and governance challenges, including corruption, that have greatly hindered progress to date,” Sullivan said.