Twelve Republican U.S. senators, including two vice presidential hopefuls and Senate Minority Leader Mitch McConnell, R-Ky., signed a letter threatening International Criminal Court officials and their family members with sanctions and other penalties if they move forward with international arrest warrants against Israeli leaders over the war in Gaza.

“Target Israel and we will target you. If you move forward with the measures indicated in the report, we will move to end all American support for the ICC, sanction your employees and associates, and bar you and your families from the United States,” read the April 24 letter made public on Monday. “You have been warned.”

The letter to ICC chief prosecutor Kraim Khan was led by Sen. Tom Cotton, R-Ark., and McConnell and signed by Sens. Marsha Blackburn, R-Tenn., Katie Britt, R-Ala., Ted Budd, R-N.C., Kevin Cramer, R-N.D., Ted Cruz, R-Texas, Bill Hagerty, R-Tenn., Pete Ricketts, R-Neb., Marco Rubio, R-Fla., Rick Scott, R-Fla., and Tim Scott, R-S.C. Rubio and Tim Scott are widely considered to be possible running mate picks by former President Donald Trump.

Khan’s office did not immediately return a request for comment, but denounced attempts to intimidate it last week.

The senators argued Israel’s actions in Gaza are “legitimate actions of self-defense” against Hamas, who triggered the war with an Oct. 7, 2023, attack on southern Israel that killed around 1,200 and led to the abduction of around 250 hostages. They also said penalizing Israel would undermine the country’s legal system and questioned why the ICC has not issued arrest warrants for Iranian Supreme Leader Ayatollah Ali Khamenei, Syrian President Bashar al Assad, Hamas leaders or Chinese President Xi Jinping.

“To be clear, there is no moral equivalence between Hamas's terrorism and Israel's justified response,” the senators wrote.

What the ICC is or is not investigating remains nonpublic for now, but opponents of Israel’s war effort in Gaza have labeled it a genocide, pointing to the cut off of humanitarian aid into an enclave that the U.N. says is experiencing “full-blown famine,” as well as the destruction of schools, hospitals and cultural sites, and the killings of at least 34,735 people, around two-thirds of whom are women and children, according to local health officials. 

On Monday, experts at the U.N. “condemned the continued and systematic onslaught of violence committed against Palestinians in Gaza, with most victims being women and children over the past seven months.” They said over 390 bodies have been found in mass graves at Gazan hospitals, “including of women and children, with many reportedly showing signs of torture and summary executions, and potential instances of people buried alive.”

The ICC, which officially launched in 2002 at The Hague, is charged with investigating genocide, war crimes, crimes against humanity and the crime of aggression. As a “court of last resort,” its mandate is to step in and prosecute governments and individuals when countries’ judicial systems are unable to act, though it has no enforcement mechanism. While 124 states have signed onto the Rome Statute that empowers the ICC, the U.S., Israel, Russia and China are among the dozens of countries who have not. The State of Palestine, which is recognized by 139 U.N. member states but not the U.N. itself or the United States, signed onto the statue in 2015.

The court has not announced charges or detailed any investigations connected to the Israel-Hamas war, but issued a statement last week as pressure from Israeli Prime Minister Benjamin Netanyahu, U.S. House Speaker Mike Johnson, R-La., and other top U.S. and Israeli officials mounted over reports the ICC was considering issuing arrest warrants.

“The Office of the Prosecutor is aware that there is a significant public interest in its investigations, and it… seeks to engage constructively with all stakeholders whenever such dialogue is consistent with its mandate under the Rome Statute to act independently and impartially,” Khan’s office said. “That independence and impartiality are undermined, however, when individuals threaten to retaliate against the Court or against Court personnel.”

The statement noted it was a violation of international law to threaten retaliation against ICC officials or to attempt to prevent them from performing their duties.

“The Office insists that all attempts to impede, intimidate or improperly influence its officials cease immediately,” the statement concluded.

In remarks last week, Netanyahu called the potential warrants “an outrage of historic proportions” and that he “expects the leaders of the free world… to use all the means at their disposal to stop this dangerous move.” Johnson in a statement called the reports “disgraceful” and urged President Joe Biden to “use every available tool to prevent such an abomination.” On Friday, White House press secretary Karine Jean-Pierre said the administration opposes “any threats or intimidation to public officials,” but that the president does not “support this investigative probe. We do not believe it’s within their jurisdiction.”

Israel’s Foreign Ministry said late Sunday that it had informed missions abroad of “rumors” that the court could order the arrest of senior Israeli political and military officials. The ministry did not give a source for the rumors.

Khan visited Ramallah and Israel in December, meeting Palestinian officials and families of Israelis killed or taken hostage by Hamas militants in the Oct. 7 attack that sparked the Israel-Hamas war.

Khan called Hamas’ actions “some of the most serious international crimes that shock the conscience of humanity, crimes which the ICC was established to address,” and called for the immediate and unconditional release of all hostages.

Khan said “international humanitarian law must still apply” in the Israel-Hamas war and “the Israeli military knows the law that must be applied.” After the visit, Khan said an ICC investigation into possible crimes by Hamas militants and Israeli forces “is a priority for my office.”

In 2020, then-President Trump slapped economic and travel sanctions on the ICC prosecutor and another senior prosecution office staffer. The ICC staff were looking into U.S. and allies’ troops and intelligence officials for possible war crimes in Afghanistan.

Biden, whose administration has provided crucial military and political support for the Gaza offensive, lifted the sanctions in 2021.

The ICC has 17 ongoing investigations, has issued a total of 42 arrest warrants and taken 21 suspects into custody. Its judges have convicted 10 suspects and acquitted four.

In its early years, the court was criticized for focusing on crimes in Africa — 10 of its investigations are in African nations — but now it has investigations in Asia, Europe, the Middle East and Latin America.

In March 2023, after the court issued a warrant for Russian President Vladimir Putin on charges of responsibility for the abductions of children from Ukraine, Russia responded by issuing its own arrest warrants for Khan and ICC judges. At the time, Biden praised the move by the court and, reportedly, ordered his administration to share evidence of Russian war crimes with the ICC.

“I think it's justified… It's not recognized internationally by us either. But I think it makes the very strong point,” Biden said. “He’s clearly committed war crimes.”

The Associated Press contributed to this report.