House Speaker Paul Ryan on Friday said he was “heartened” by progress and urged patience on President Trump’s strategy in Afghanistan following a two-day fact-finding tour of the country.

Afghan special forces and their commando troops have suffered significant casualties, but they are persevering against the Taliban following a decision by Trump last year to send an additional 4,000 troops to assist, Ryan said.

The speaker made the trip with Rep. Mac Thornberry, R-Texas, the House Armed Services chairman, to assess the new strategy as the war enters its 18th year. The two lawmakers traveled to three military camps in the country and met with senior leaders including Gen. Scott Miller, the new commander of U.S. forces there, and Afghan President Ashraf Ghani.

“After this visit, it is clear to me that the president’s South Asia strategy must be given an opportunity to succeed,” Ryan said. “Fighting terrorism in this region remains in our nation’s vital interest and it is clear the current momentum of our military campaign is underpinning our diplomatic efforts to set the conditions for reconciliation.”

Trump announced in August 2017 he would send additional troops after months of internal debate within the administration. The extra forces, as well as a regional approach applying pressure on Pakistan, is aimed at forcing the Taliban into a peace agreement.

Over the past year, the country has seen an uptick in violence and Taliban forces have staged major attacks on provincial centers. The group waged a dayslong siege in August on the city of Ghazni that resulted in tough fighting with Afghan forces backed by U.S. troops.

Afghan officials have estimated about 30-40 members of the Afghan security forces are killed per day on average, according to a recent New York Times report.

When confronted with a report that 500 were killed in August, Defense Secretary Jim Mattis said the figures sounded about right but denied that the losses are unsustainable and that the U.S. might be on the verge of losing a war of attrition.

“The Afghan Army has taken severe casualties over the last year and a half. They've stayed in the field fighting,” Mattis said during a rare press gaggle late last month.

The U.S. invaded Afghanistan in 2001 following the al Qaeda terror attacks of 9/11. As the war has continued, the U.S. has also worked for more than a decade to secure the country by building up army and national police forces controlled by the government in Kabul.