In an exchange with reporters on Thursday, Defense Secretary Ash Carter conceded that the US government’s plans in Syria open the door to more US military involvement in the country’s long ongoing civil war.

“Of course we would have some responsibility to protect forces,” the defense chief said, referring to rebel militants backed by Washington that should be deployed to Syria in “a few months.”

Carter also noted that while the Pentagon expects the vetted-rebels to primarily engage with Islamic State forces in Syria, he said the American military has some responsibility to aid them if they’re “contested by regime forces.”

Whether that assistance would come in the form of airstrikes, which are already underway inside Syria, or through a new avenue, is still a matter up for internal deliberation, Carter added.

“We have not decided yet in detail how we would exercise that responsibility but we have acknowledged that we have that responsibility,” Carter said.

In January, the Pentagon announced it was dispatching hundreds of troops to Turkey, Qatar, and Saudi Arabia to train and equip Syrians that US intelligence agencies had deemed to be part of the “moderate opposition.” On Thursday, officials in Jordan said coalition forces had begun training at least 400 vetted Syrian rebels within its borders as well, according to The Guardian.

During a Senate hearing on Wednesday, Carter described it as a “third force to combat [ISIL and Assad forces] and to create an environment in which the Syrian people can leave in peace, which they deserve,”

Pentagon officials have said on numerous occasions that the train and equip mission is a multi-year effort—a tacit acknowledgment that US policy is to expect the already brutal war to rage on for more years to come.

When asked on Thursday how the defense department will ensure that this new rebel force will not commit war crimes once deployed to the battlefield, Carter pointed to a strict training regiment.

“[An] explicit part of their training is how to conduct themselves in a way that is consistent with international law,” he claimed, saying that a disposition to commit atrocities was also part of the vetting process.

Carter added that “continued support for [the rebels] would be strongly conditioned upon their continued good conduct in that regard.”