GREEN VILLAGE BASE, EASTERN SYRIA — U.S. troops in Syria have picked up the pace of counterterrorism operations following a lull, a top U.S. commander said Saturday, but the future of the American mission remains uncertain amid changing dynamics in the Syrian conflict and the potential for renewed presidential intervention.

“The tempo is coming back,” Gen. Kenneth “Frank” McKenzie Jr., who heads U.S. Central Command, said during a visit to a constellation of tiny American outposts in eastern Syria.

American troops in Syria, like those in neighboring Iraq, shifted their focus from anti-extremist operations to force protection after a Jan. 3 strike in Baghdad killed Maj. Gen. Qasem Soleimani, Iran’s most influential military figure. Iran retaliated by launching ballistic missiles at U.S. troops in Iraq, causing no deaths, although a number of service members have suffered symptoms believed to be associated with traumatic brain injury.

Now, McKenzie said, U.S. troops are conducting three to four operations a week with Syrian Kurdish forces against the Islamic State, an increased pace but still far fewer than during the earlier massive multinational campaign.

McKenzie touched down at a series of isolated bases, where 500-600 American troops are arrayed, in his first visit to an area of Syria known as the “eastern security zone.” Home to valuable oil facilities, the swath of scrubland and farms became a focus for U.S. operations after a Turkish invasion into northern Syria pushed U.S. troops from bases there.

But even as McKenzie provided assurances that the U.S. military remained intent on battling the Islamic State and mentoring the Kurdish-dominated Syrian Democratic Forces (SDF), he gave no timeline for how long Americans will remain.

“I frankly don’t know how long we’re going to be here,” said Mc­Kenzie, who met with U.S. commanders and with Gen. Mazloum Kobane, commander of the SDF, which has been the primary American partner in Syria.

“And I have no instructions other than to continue to work with our partner here,” he said, against the Islamic State and protecting oil infrastructure the Trump administration hopes will help fund the SDF’s ongoing security work.

For now, American commanders are hoping to accomplish as much as possible, in further weakening the Islamic State and in transforming the SDF into a sustainable internal security unit before larger forces bring about a U.S. withdrawal.

That could include orders from President Trump, who has promised to end America’s counterinsurgency wars and extricate the United States from the Middle East. Twice, he has appeared to order a full withdrawal from Syria and then backed away.

The president has permitted the mission to continue to prevent militants from regaining control of Syrian oil fields, but Pentagon leaders know he could change his mind at any moment.

It might also include what is expected to be an eventual campaign by Syrian President Bashar al-Assad, who with Russian backing has clawed back many areas of Syria previously under opposition control, to press east into areas now under U.S. and SDF control.

“We’ll be prepared to deal with that as those events develop in the future,” McKenzie said. “Now we’re firmly focused on the lasting defeat of ISIS.”

One of the bases used to coordinate that effort is Green Village, an outpost where U.S. troops are housed in former oil industry villas next to a major Syrian oil field. Another base, called Conoco, sits amid massive storage drums, a symbol of the Kurds’ ambitions to gain financial autonomy. The fields under Kurdish control are not working close to full capacity, U.S. officials said.

The Washington Post, which along with the Associated Press accompanied McKenzie during his trip to Syria, is withholding the names of other American facilities at the request of the U.S. military.

Outside those bases’ barbed-wire and dirt-filled barriers, the Syrian conflict is increasingly complex in ways that could affect U.S. troops and their mission. Officials say that American forces continue to come into proximity, primarily on local highways, to Syrian government and Russian troops who have moved deeper into eastern Syria, but that those encounters have not produced hostilities.

The SDF is now coordinating with Russia in some areas that U.S. troops vacated last fall, as the group seeks to make arrangements with the Assad regime that would allow it to retain some degree of autonomy as the government attempts to reassert control.

Iran could also attempt further retaliation against the United States via proxy groups or its own military forces in Syria.

Another dynamic that could affect the duration of the American presence is found in Idlib, a province in the northwest where Syrian and Russian forces are conducting a fierce bombing campaign to stamp out a remaining bastion of regime opposition.

U.S. officials anticipate that Assad and Russia may become mired in a lengthy, bloody campaign that could prevent the ­regime from moving into areas where the SDF and Americans are present, potentially allowing the United States to continue its campaign against Islamic State remnants for longer.

McKenzie said that Idlib could become a “massive humanitarian tragedy.” He said the area was home to militants and also ordinary Syrians.

“I’m afraid that many innocent people are going to be lost,” he said.