Bill comes as Arab governments move to rekindle relations with al-Assad government after years of diplomatic isolation.

In a statement on Thursday, Tlaib said that victims of Syria’s civil war have not yet received justice, with perpetrators facing few consequences.

“Assad’s regime committed some of the worst atrocities of the 21st century during the country’s civil war that began in 2011,” Tlaib said in the statement.

“These include but are not limited to the use of sarin gas and other chemical weapons against civilians, the widespread use of torture, and the deliberate targeting of civilians with conventional weapons.”

The bill comes as Arab governments move to bring the Assad regime in from the cold after years of diplomatic isolation. But the US, under the administration of President Joe Biden, has insisted that it will not follow in their footsteps.

The Syrian civil war began as a series of uprisings against the repressive policies of the Assad government, but the conflict grew, drawing in numerous foreign powers and militant groups. It has since displaced nearly half of Syria’s pre-war population and killed about half a million people.

Thursday’s statement from Tlaib and Omar says that their bill is designed to encourage the US to throw its weight behind efforts to create international justice mechanisms to hold the Assad government accountable.

“The international community has previously established ad hoc tribunals, special courts, and other justice mechanisms through the United Nations to bring justice in specific countries where there have been war crimes,” their statement reads.

“Given the sheer number and scale of the atrocities committed during Syria’s civil war, an international justice mechanism is clearly necessary.”

Last month, war crimes investigators concluded that the Syrian government had deployed “shabbiha” militias to clamp down on dissent, using methods such as torture and sexual violence against perceived opponents.

In June, Syrian survivors of “enforced disappearances” — which can involve arrests, detentions and abductions done in secret — also called on the United Nations to support efforts to locate the roughly 100,000 Syrians who remain missing and bring perpetrators to justice. Enforced disappearances are considered a crime against humanity under international law.

However, as Assad has cemented his control over large swathes of the country, leaders across the Arab world have taken steps to repair ties with the Syrian government that were damaged or broken off during the war.

In May, the Arab League made the controversial decision to reinstate Syria’s membership after suspending it more than 10 years ago. Critics of Assad’s administration expressed dismay at the decision, seeing it as a vindication of the methods used by his government.

Tlaib and Omar, members of a group of progressive US legislators, have been vocal critics of alleged rights abuses committed in Syria, as well as in US allies such as Israel, Egypt, India and Saudi Arabia.

Earlier this week, they boycotted a speech given by Israeli President Isaac Herzog before members of Congress, citing accusations by Palestinians and numerous human rights groups that the Israeli government is perpetuating the crime of apartheid.

Last month, Omar and Tlaib also boycotted a speech before Congress by Indian Prime Minister Narendra Modi, whose government has been accused of stifling dissent and encouraging violence and discrimination against minorities.