Afghan commandos with the 7th Special Operations Kandak practice moving wounded soldiers to an Afghan Air Force helicopter at Camp Bastion, Helmand Province. (Thomas Gibbons-Neff/The Washington Post)

The United States will send an additional 3,500 troops to Afghanistan, U.S. officials said Wednesday. The long-expected deployment would bring the total number of American troops in the country to more than 14,000.

Last week, Secretary of Defense Jim Mattis told reporters that he had signed deployment orders for some of the troops but would not make an announcement on the specific numbers until after he briefed Congress. On Wednesday, Chairman of the Joint Chiefs of Staff Gen. Joseph F. Dunford Jr. met on Capitol Hill with lawmakers during a closed-door session. The officials who said that Mattis had approved the roughly 3,500 additional forces spoke on the condition of anonymity to discuss troop numbers that had not been released by the Pentagon. Reuters was first to report on the development.

It is unclear what the additional U.S. forces plan to accomplish in the nearly 16-year-old war and how long that might take. Last month President Trump outlined a broad strategy for Afghanistan and the surrounding region, saying that “conditions on the ground — not arbitrary timetables” would guide his administration’s approach. He also said that he would take a stronger stance against Pakistan — a country long accused of harboring militants within its borders — and that American forces would “have the necessary tools and rules of engagement to make this strategy work.”

While President Barack Obama approved more aggressive airstrikes against the Taliban in 2016, Trump’s new rules of engagement could allow U.S. forces to target Taliban forces faster than they have in the past and attack them even if they are not directly threatening Afghan forces, according to U.S. officials familiar with the possible changes who spoke on the condition of anonymity because the changes had not yet been authorized.

The Obama-era change, dubbed “strategic effects,” allowed U.S. forces to strike Taliban fighters if the airstrike would change the outcome of a ground battle. Trump’s adjustments to the rules of engagement would — in short — allow American aircraft to strike the Taliban wherever they might appear.

[U.S. airstrikes in Afghanistan are at levels not seen since Obama troop surge]

At the war’s height in 2011, more than 100,000 U.S. troops were based in Afghanistan, along with thousands of NATO allies. Now there are roughly the same number of American forces in the country as there were in 2004, three years after the United States invaded. The current military forces, along with the tens of thousands of civilian contractors, are mostly there to help train the struggling Afghan military and help them defend their territory. Several thousand of U.S. troops are also involved in a counterterrorism mission that targets groups such as al-Qaeda and the Islamic State.

More than 2,000 Americans have died in Afghanistan since 2001, and 10 U.S. troops have been killed by hostile fire this year. More than 1,600 Afghan civilians had been killed from Jan. 1 to June 30, according to a July report from the United Nations.

On Wednesday, a suicide bomber detonated in front of the largest U.S. base in the country — Bagram Airfield — after American and NATO forces dropped religiously offensive leaflets in surrounding countryside. A statement by the U.S.-led mission did not detail the extent of the damage, only that there was a “small number” of casualties.