President Trump on Thursday vowed that the United States would prevent the Islamic State from regaining control of oil fields in eastern Syria, emphasizing his interest in the energy assets there despite his steps to curtail the U.S. military mission in the country.

“We will NEVER let a reconstituted ISIS have those fields!” Trump said on Twitter, using an acronym for a group that the U.S. military and Syrian Kurdish forces have largely defeated. “Perhaps it is time for the Kurds to start heading to the Oil Region!”

The president has repeatedly referred to the oil-producing areas of Syria as he defends his abrupt decision to withdraw most American forces, a move that critics say has enabled a militant resurgence and endangered a battlefield ally.

Trump’s latest comments came as the Pentagon considers a plan that would place heavy weaponry around the oil fields and retain a larger number of troops than officials have previously suggested, potentially further diluting the practical effect of the announced withdrawal.

The evolving plan underscores the ongoing security threats in Syria and, potentially, White House sensitivity to a congressional rebuke. It also highlights that the U.S. mission appears to be shifting from one focused on fighting the Islamic State to at least partly keeping the country’s own government from possessing all its oil fields.

Earlier this month, Trump announced that he would withdraw most U.S. troops from Syria ahead of a Turkish offensive against the Pentagon’s partner force there, the Kurdish-led Syrian Democratic Forces (SDF). Trump said the region was safer than before and declared a “victory,” even as chaos ensued and Russian and Syrian government troops took over territory once held by the United States and the SDF.

Now, as Pentagon officials express concern that the situation could allow Islamic State militants to regain strength, administration leaders are discussing options, including using tanks and associated U.S. troops to protect oil fields in eastern Syria that are now under SDF control.

One U.S. official, who spoke on the condition of anonymity because of the sensitivity of the issue, said such an operation would be likely to require about a company of U.S. troops initially, including a couple hundred service members, a handful of tanks and supporting equipment.

“It is an option,” the official said. “It will be based on what is in theater and what can be moved.”

Nicholas Heras, a fellow at the Center for a New American Security, said the U.S. military has had troops stationed alongside SDF forces at sites close to oil fields in Syria’s eastern Deir al-Zour province.

The Islamic State’s ability to use the fields to generate significant revenue ended after SDF fighters, backed by the United States, captured the most important oil-producing area in 2017. But its energy resources have attracted inter­national attention since then. In 2018, Russian mercenary forces aligned with the Syrian regime were killed during a clash with U.S. and Kurdish troops stationed near a Conoco gas plant. That attack was repelled with U.S. airstrikes.

Officials acknowledged that sending tanks might require additional service members for security and support. The officials said that the deployment of other heavy equipment, such as Bradley Fighting Vehicles, was also under consideration.

The official described the plan for tanks, first reported Wednesday night by Newsweek, as a “complete change in macro approach” for the U.S. military in Syria. “You can’t make up this stuff,” the official said.

Heras said that supplying and protecting military bases in that area could be difficult as the overall U.S. presence dwindles.

Comments from fellow Republicans on Thursday appeared to confirm that the president may be preparing to adjust his plan for Syria.

The administration has already gone from saying that all U.S. forces partnered with the SDF would leave to making plans for a residual force to remain alongside them in oil areas.

Ron Johnson (R-Wis.), the chairman of the Senate Homeland Security Committee, said he was encouraged after attending a small White House briefing that was led by Army Gen. Mark Milley, the chairman of the Joint Chiefs of Staff, and attended by Trump. Defense Secretary Mark T. Esper, who is traveling in Europe, took part in the briefing remotely, lawmakers said.

“We will leave troops there to make sure that Iran does not, Russia doesn’t get, Assad doesn’t get those oil wells,” Johnson said. “To the extent anybody benefits from it, it will be our Kurdish allies. I think that’s a really good sign that we are not abandoning the Kurds.”

Sen. Lindsey O. Graham (R-S.C.), who has argued that the United States must not allow Kurdish partners to be abused by Turkey, described the briefing as promising. “I think there’s a plan coming together that I could support,” he said.

A defense official, who spoke on the condition of anonymity because he was not authorized to comment on the record, said Esper was making recommendations to Trump that he thought were necessary to ensure the Islamic State remains suppressed.

“The U.S. is committed to reinforcing our position, in coordination with our SDF partners, in northeast Syria with additional military assets to prevent those oil fields from falling back to into the hands of ISIS or other destabilizing actors,” the official said.

Violence in several parts of northern Syria on Thursday underscored the challenges ahead in the volatile region, despite Turkey’s recent agreements with the United States and Russia aimed at calming the fighting.

The SDF on Thursday accused Turkey and its allies of attacking three villages south of the Syrian border town of Ras al-Ayn and violating a recent cease-fire. The SDF said the villages, which had been attacked with artillery and ground forces, were outside the cease-fire area.

Turkey did not comment directly on the accusations but said that five of its soldiers were wounded Thursday in “drone, mortar and light weapons attacks” in Ras al-Ayn. The soldiers were “conducting reconnaissance-surveillance activities,” a Turkish Defense Ministry statement said, and “the required response was given within the framework of self-defense.”

Syria’s state news agency said Thursday that Syrian government troops had been attacked by the Turkish military and its allies around the town of Tal Tamr, about 18 miles south of the Turkish border. A Syrian government statement said that Syrian forces had “inflicted casualties among the aggressor forces.”

Fahim reported from Istanbul. Paul Kane contributed to this report.