NATO Secretary General Jens Stoltenberg, Defense Secretary Jim Mattis and British Secretary for Defense Gavin Williamson during a NATO defense ministers meeting at the Alliance’s headquarters in Brussels on Nov. 8, 2017. (Eric Vidal/Reuters)

BRUSSELS — Senior U.S. defense officials pressed their case Thursday for fellow members of the North Atlantic Treaty Organization to contribute more troops to the Afghanistan war effort, but the response is still short of what top coalition commanders say they need.

NATO Secretary General Jens Stoltenberg said that the new number is not yet finalized, but acknowledged that not all NATO military jobs in Afghanistan have been filled — a persistent problem last year when there were hundreds of vacancies.

“We still have some gaps that we are continuing to work on, and we will address them with allies and partners so that we have a troop level, and not only the number of troops, but the type of troops we need to have a mission in Afghanistan next year,” Stoltenberg said at a meeting of NATO defense chiefs in Brussels.

President Trump announced Aug. 21 that instead of pulling U.S. troops out of Afghanistan — as he claimed his instinct said — he was adding several thousand more while loosening the restrictions on battlefield operations. Trump said that he was not interested in nation-building, but wanted an “honorable and enduring outcome worthy of the enormous price that so many have paid” in the war.

As part of that, Trump sent about 3,500 more U.S. troops to fill specific needs, including additional air power, precision rocket fire and medical evacuation. Some of those troops are devoted to the NATO mission that trains Afghan forces, known as Resolute Support, while others are assigned to a separate U.S. counterterrorism mission called Freedom’s Sentinel. The Pentagon has declined to provide a new breakdown on how many are assigned to each.

Army Gen. John W. Nicholson Jr., the top U.S. commander in Afghanistan, told reporters in Brussels that the entire “uplift” in U.S. troops approved by Trump has arrived. That puts the total number of American troops in the country at about 14,500, with a few thousand devoted to the counterterrorism efforts.

But there remains an unresolved debate about why other NATO nations are not able to fill minimum requirements set forth by coalition commanders in Afghanistan and approved by the alliance. Nicholson has urged NATO for months to fully support what is known as the Combined Joint Statement of Requirement, a detailed breakdown of what is needed in the war effort, but the allies are still short of doing so.

What country that has stepped forward is Turkey. A Turkish official, speaking on condition of anonymity due to the sensitivity of the discussions, said that the nation will add an additional 50 troops to serve as advisers at Afghan military training centers, and 47 to man a “quick-reaction” rescue based at the airport in Kabul. They also may add additional police trainers and troops who maintain aircraft.

U.S. Army Gen. Curtis M. Scaparrotti, the supreme allied commander of NATO, said that the military alliance will fill Nicholson’s troop requirement “substantially, in a very satisfactory way in my mind.” He acknowledged there are shortfalls, but declined to say what percentage of the jobs will remain vacant.

The continued shortfall comes despite Trump taking a pointed approach to NATO this year, saying that its members must increase their defense spending. Several have done so.

The shortfall also comes despite months of pressing by Nicholson. In 2017, about 20 percent of the jobs required in the NATO training mission were vacant, “the lowest level of capability that we’ve ever had in the 16 years” since the Sept. 11, 2001, attacks, he said. Nicholson said that he is now looking for a minimum of about 15,800 troops for the Resolute Support training mission, counting Americans.

A U.S. Marine provides security at the Helmand Provincial Police Headquarters in Lashkar Gah, Afghanistan, on July 9, 2017. (Photo by Sgt. Justin T. Updegraff/ Marine Corps)

“This is the minimum manning requirement for the mission,” Nicholson said. “So, I’ve only been at 80 percent of that minimum number, and that’s why we’ve had a higher level of risk.”

Nicholson said that many nations offering additional troops in Brussels this week still have to go through their own approval processes at home, making it difficult to determine how many additional troops will be going to Afghanistan. The process, he said, is “still playing out.”

The additional NATO troops will primarily be devoted to advising Afghan police and commandos, overseeing schools to train them and building the Afghan air force. There is a potential that contractors could fill some of the shortfall, Nicholson said, but he added that he prefers not to do so.

Scaparrotti, asked if a shortfall in NATO troops would require additional Americans in Afghanistan, said that he “wouldn’t look at it that way.”‘ The United States has contributed troops to both the NATO mission and the U.S. counterterrorism mission based on Nicholson’s stated needs, and made other requests from the allies.

“It’s a bit different in that respect in terms of what we ask them to do, and I think the nations have responded well,” Scaparrotti said.

The new approach in southern Asia includes fighting the Taliban while remaining open to reconciliation with them if they change their behavior. It also calls for taking a tougher stance with Pakistan, which has long been accused of supporting the militants from across their shared border.

Defense Secretary Jim Mattis, asked for specifics Thursday about what the new strategy with Pakistan, said that he wants countries across the region “working from the same sheet of music.” There are ways to reward Pakistan for cooperating, and ways to “hold them to account” if they do not, Mattis said, without providing examples.

“Principle going into this is that we are going to work with Pakistan and make this work so that there is no longer a threat coming across the border there,” Mattis said. “This is an international effort. This isn’t an American-alone effort.”

Nicholson said the United States is preparing for Afghan forces to go on the offensive against the Taliban more in 2018, and will be able to do so because they will have more commandos and a larger air force of their own. That’s part of the broader effort to force the Taliban to the negotiating table and end the conflict.

“This is a fight and talk approach,” Nicholson said. “We’re encouraging the enemy to engage in these conversations as we increase the pressure.”

Michael Birnbaum in Brussels contributed to this report.