BRUSSELS — Nearly three years after the North Atlantic Treaty Organization ended combat operations in Afghanistan, the 29-nation alliance will send troops once more into the country with hopes that the renewed surge will help the Afghan military beat back a resurgent Taliban.

Speaking ahead of a defense ministerial meeting here Thursday, NATO Secretary General Jens Stoltenberg said thousands of troops have been requested, but he did not say how many would deploy.

With the Taliban in control of broad swaths of the country and the Afghan military locked in a primarily defensive war, it is unclear how a new infusion of NATO or U.S. forces could radically turn the tide of the conflict.

“Fifteen nations have already pledged additional contributions to Resolute Support Mission. And I look forward to further announcements from other nations,” Stoltenberg said, using the name of the NATO mission to Afghanistan.

Stoltenberg stressed that NATO’s renewed presence did not mean the beginning of another combat mission; instead, he said, the alliance will focus on building the Afghan special operation forces, air force and other military training institutions.

“We don’t think this operation in Afghanistan is going to be easy and we don’t think its going to be peaceful … this year or next year or in the near future,” he said during a news conference Thursday afternoon. “As long as the Taliban believe they can win the war they will not negotiate. We need to break the stalemate and to enable the Afghans to make advances.”

Stoltenberg’s remarks come as the United States weighs its own commitment in what has become its longest-running war. In recent weeks, President Trump delegated authorities to the Pentagon to set troop levels in Afghanistan, and Defense Secretary Jim Mattis has pledged to present a strategy to Congress by mid-July. Earlier this month, the retired four-star Marine general told lawmakers that the United States was “not winning,” and battlefield commanders, including the head of U.S. forces in Afghanistan, Gen. John Nicholson, have requested a “few thousand” more troops.

Mattis said Thursday during a news conference that he had received 70 percent of the commitments from NATO countries for his upcoming strategy and was confident that he would be able to secure the rest in the coming weeks. Mattis gave no timeline for America’s renewed commitment to Afghanistan and suggested that NATO had drawn down too early in 2014.

“It’s not like you can declare a war over,” Mattis said. “What is the price of not fighting this war? And in that case we’re not willing to pay that price.”

With a Taliban insurgency that has proven resilient despite heavy battlefield losses, lawmakers in Washington and some NATO allies remain wary of any new military solution in Afghanistan.

In an interview, Canadian Defense Minister Harjit Sajjan said his country has received the request for more troops but has not yet decided to pledge any additional forces.

Canadian soldiers withdrew from Afghanistan completely in 2014, after participating in several bloody campaigns around Kandahar in 2006 and a limited training mission after 2011. Between 2001 and 2014, more than 150 Canadian troops died in Afghanistan.

With no physical presence in the country, Canada has instead continued to provide financial support to the Afghan security forces.

“Afghanistan is obviously very important to us, and we’re going to monitor the situation,” Sajjan said. “The military is not going to give you that complete victory. It takes an entire whole of government approach for it; the real solution will come from the political side.”

British Defense Secretary Michael Fallon told a group of reporters during the ministerial meeting Thursday that Britain was in Afghanistan “for the long haul” and would send just under 100 additional troops to help prop up Afghan forces around Kabul, bringing the total number of British soldiers in the country to around 600. In the last year, the Afghan capital has been rocked by a spate of terrorist attacks that have killed hundreds.

Mattis said he would take what he learned from his NATO counterparts at the defense ministerial back to Washington and deliver his formal strategy to Trump in the coming weeks.

Currently there are roughly 13,500 NATO and U.S. troops in Afghanistan. The Americans number around 8,500 and are split between counterterrorism operations and supporting the NATO-led training mission. At the war’s height in 2010 and 2011 there were more than 100,000 U.S. forces in Afghanistan.

More than 2,000 U.S. troops have died in Afghanistan since 2001, and Afghan security forces continue to take an almost unsustainable amount of casualties despite U.S. air support. Civilians, however, have borne the brunt of the violence, with 2016 marking the deadliest year for the Afghan population since the United Nations mission to the country began monitoring the statistics in 2009.

Michael Birnbaum contributed to this report. This story was originally published at 9:17 a.m. and updated to include remarks from Defense Secretary Mattis and other officials in Brussels.

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