General Joseph Votel, the head of the US Central Command (Centcom), visited Syria to meet with forces fighting the Islamic State (Isis) – becoming the highest ranking American military officer to enter the country since the campaign to counter the militant group began.
"There's nothing like being able to see it up front and talk to the people who are actually doing it," he told reporters on his return. "So it was a good day for me."
He added: "We had the opportunity to get around and see a number of things, talk about a wide variety of topics, talk about how things are going [and] talk about things that we could do to continue to increase our cooperation, collaboration and effectiveness."
Without specifying exactly who he met, the four-star US Army General said he had been briefed by "some of the Syrian Democratic Forces [SDF] leadership in multiple locations".
He said: "We will see progress. We will also see setbacks. There's a lot of unpredictable stuff out here.
"The enemy always has a vote in the things we're doing and they will always react. And this is an enemy that does react and does adapt and does change to the situation on the ground."
He added: "One of the things that we as military members have to do, is we have to respect our enemy. The things they do are abhorrent."
General Votel has served for two years as head of Centcom, which covers the central area of the globe between the European, Africa and Pacific Commands. He said he was "incredibly "proud of how our coalition members here who are working with our partners are doing in very challenging environment, but they are definitely rising to the occasion."
He added, "They're exhibiting their initiative, their innovativeness, their skills [and] their expertise to really make a difference here."
As well as visiting Syria, General Votel also held meetings with Kuwaiti defence minister, Khaled Al Jarrah Al Sabah, and discussed "upcoming operations" with the Iraqi army's chief of defence and staff.
He said they discussed "a few things that they are looking for assistance on and that we are…working with them on as they continue to maintain momentum" in the fight against Isis (Daesh).
After a visit to Taji - a rural district situated around 27 miles north of the Iraqi capital Baghdad - Votel said coalition trainers from Australia and New Zealand were "doing some great work in very challenging conditions here, to help the Iraqis get ready for the operations that are upcoming."
However, he said one of the biggest challenges faced by both Iraqi and the coalition was the generation of forces.
"There's a lot going on," he said, adding they had operations in the Anbar Province, part of which borders Syrian and the Tigris River Valley, as well as around the capital, Baghdad.
"They're having to make decisions in terms of where their force is going, where their priorities are, how they sustain those things [and] how they move forces around and get them ready to continue their offensive operations so they can maintain momentum," he said.
"That's a difficult challenge for any military," he added. "But I think it's one that they are working through and we are seeing some success with it."