WASHINGTON (CN) – With the Trump administration’s Syria policy still unclear, House lawmakers heard from experts Thursday who urged a course of action that will remove Syrian President Bashar al-Assad from power.

House Foreign Affairs Committee Chairman Ed Royce echoed that position, calling for U.S.-backed forces to confine Assad in western Syria as they gain ground in the east.

This could open up sanctuaries for Syrians to find refuge and establish basic governance, Royce said. “From there, the United States and our allies must work together to advance a plausible vision of a post-Assad Syria,” the California Republican added.

Syria’s civil war – now in its seventh year – has displaced 12 million people, with nearly 500,000 dead, sparking the greatest humanitarian disaster since World War II.

The House Foreign Affairs Committee called the morning hearing to discuss policy options after the April 6 airstrikes on a Syrian airfield, which the U.S. carried out in response to a suspected sarin gas attack that the U.S. has blamed on the Syrian government.

“Assad cannot and will never be capable of putting Syria back together again,” said Charles Lister, a senior fellow at the Middle East Institute.

“Six years of mass murder, sectarian massacres, the industrialized use of torture and execution, the repeated use of chemical weapons, barrel bombs, ballistic missiles and more does not just represent extremist, radicalization gold dust,” Lister continued. “It is also clear and incontrovertible evidence that Bashar al-Assad has little to offer in terms of popular credibility or a promise of stability in Syria.”

Saying that Syria gets its chemical weapons and ballistic missiles from al-Assad’s Scientific Studies and Research Center, the Treasury Department imposed sanctions earlier this week on 271 of the center’s Syrian government employees.

More than 80 people died after the April 4 chemical-weapons attack in Khan Sheikhoun, a town in Syria’s Idlib province.

Tests and autopsies on victims who were brought to Turkey, under the monitoring of the World Health Organization, revealed evidence consistent with sarin exposure.

Setting the stage for a fierce information war, however, the Syrian government has denied responsibility for the attack

One theory that has erupted on social media, trending with the hashtag #SyriaHoax, claims that the attack was a “false flag” staged to justify U.S. intervention.

The House heard from the Middle East Institute’s Lister meanwhile that the U.S. airstrikes were “a justified, proportionate and necessary response to a flagrant war crime.”

Saying he has spent nearly every day since March 2011 trying to understand the Syrian crisis, Lister predicted that a policy of mere containment will maintain the status quo and ensure instability for a decade, or more.

The “in-between” policy Lister supports stops short of a major military intervention, but will require more punitive military strikes and intensive bilateral negotiations with Russia, which has propped up the Assad government since it intervened in the conflict in 2015.

Noting that the U.S. has spent $6.5 billion in humanitarian aid, given $400 million to the Syrian opposition and spent billions more in Syria on the campaign to defeat the Islamic State group, Michael Singh of the Washington Institute for Near East Policy said the Trump administration started out on “the right foot” by launching the cruise-missile strikes.

Singh urged the Trump administration to make clear that any more chemical attacks would prompt another U.S. military response.

Singh echoed Lister’s call for the U.S. to abandon any diplomatic solution that would allow Assad to retain power, urging the administration to focus on containing the regional instability spawned by the conflict.

That should include a U.S.-led pushback against Iran, which uses Syria to enhance its regional power, Singh added. Iran must be made to withdraw its forces and proxies, including Hezbollah, from Syria as part of any international agreement to settle the conflict, Singh said.

Dafna Rand largely echoed the justification of the U.S. missile strikes, but the National Defense University professor voiced concern that they were “entirely divorced from any strategy for U.S. engagement to resolve the Syrian crisis.”

“For targeted strikes such as these to have an impact on the overall arc of the conflict, they cannot be launched in a vacuum,” she said. “They must represent one aspect of a broader diplomatic strategy utilizing economic, political, and other security levers.”

Citing statements from Secretary of State Rex Tillerson and United Nations Ambassador Nikki Haley prior to the suspected sarin gas attack, Rand suggested that Assad may have been encouraged to use chemical weapons because the Trump administration indicated a shift in U.S. policy that would let him keep power.

Once the United States launched the cruise missiles against the airfield that U.S. officials say had set off the chemical attack, however, “these same cabinet members and other senior administration officials reversed course,” Rand said.

She called their public statements in the wake of the strike “remarkably consistent with those issued by the Obama administration, making it clear that Assad’s departure would be necessary to end the Syrian civil war.”

“It is urgent that the White House clarify U.S. policy and stand behind the need for Assad to step down, in line with the 2012 Geneva Communiqué,” Rand added.