U.S. Secretary of State John Kerry says, "Daesh is responsible for genocide." In a statement to reporters on Thursday morning, Kerry said it is essential to stop the militant group, better known in the U.S. as the Islamic State, from carrying out atrocities. (Reuters)

Secretary of State John F. Kerry formally declared Thursday that the Islamic State extremist group has committed genocide against Yazidis, Christians, Shiite Muslims and other religious minorities in its rampages across the Middle East.

After months of pressure from Congress and religious groups, Kerry issued a finding that largely concurred with a House resolution declaring the Islamic State guilty of genocide. The resolution passed 393 to 0 on Monday night

Kerry said a review by the State Department and U.S. intelligence determined that Yazidis, Christians and Shiite groups have been victims of genocide, crimes against humanity and ethnic cleansing by the radical al-Qaeda offshoot, a Sunni Muslim group also known as ISIS, ISIL and Daesh, its Arabic acronym.

“The fact is that Daesh kills Christians because they are Christians; Yazidis because they are Yazidis; Shia because they are Shia,” Kerry said in a statement he read to reporters at the State Department. “Its entire worldview is based on eliminating those who do not subscribe to its perverse ideology.”

What started out as simple protests in Syria has expanded to civil war and now an international crisis.

Kerry’s declaration, while forceful as a statement of moral principles, has little practical impact on U.S. policy or military strategy. State Department officials said that the finding imposes no new obligations beyond what is already being done but that it could “galvanize” other countries to step up the battle against the Islamic State.

The United States already is leading a military campaign against the Islamic State and is one of the prime movers behind U.N.-backed peace talks to end the Syrian civil war that aided in the militant group’s rise. The Obama administration accepted 10,000 Syrian refugees this year, largely because of concerns about the number of people being targeted and brutalized by the group.

“We have proven our willingness to step in and prevent acts of genocide,” State Department spokesman John Kirby said, citing the August 2014 U.S. military rescue of stranded Yazidis on Mount Sinjar in Iraq. “Is it going to trigger something new? No. But it very much is part and parcel of the way we have been thinking about this conflict for nigh on over a year.”

Kerry tweeted later Thursday, “Naming #Daesh’s crimes is important — but what is essential is unity to stop them. U.S. will continue to lead global effort to defeat Daesh.”

In perhaps the most consequential part of Kerry’s remarks, he vowed that the United States would support efforts to document atrocities committed by the Islamic State in Syria and Iraq. While saying he was “neither judge nor prosecutor nor juror,” Kerry said the United States would “do all we can” to hold the perpetrators of genocide accountable in a court of law.

State Department officials said the United States has talked at the U.N. Security Council about referring cases to a venue such as the International Criminal Court at The Hague. But groups that had urged Kerry to make the genocide designation said they hoped the effort would now transcend talk.

“As long as we pursue that, and it’s not an empty promise and there’s not a circular debate in the Security Council, this designation from that alone could have real significance,” said Cameron Hudson, director of the Simon-Skjodt Center for the Prevention of Genocide. “This case has always been about, can a terrorist group also be a genocidal group?”

The formal finding of Islamic State genocide is important to some Christian conservatives in the United States. Many political television ads and statements by members of Congress highlighted the importance of acknowledging the genocide of Christians.

In his statement, Kerry went to great lengths to mention atrocities committed against a broad swath of religious and ethnic minorities, including Kurds, Shiites and Turkmens as well as Christians. That was because he does not want to fuel perceptions that the United States is engaged in a modern-day Crusade, a so-called clash of civilizations between Muslims and Christians, aides said.

The State Department had indicated Wednesday that Kerry would miss Thursday’s congressionally mandated deadline for the announcement because he needed more information, prompting sharp criticism from lawmakers.

But Kirby said the finding was not affected by last-minute calls from members of Congress. “The pressure to keep working through and into the night was self-imposed,” he said.

Kerry’s declaration Thursday appeared to mollify some congressional critics.

“The United States has now spoken with clarity and moral authority,” said Rep. Jeff Fortenberry (R-Neb.), a sponsor of the congressional resolution that passed Monday. “I sincerely hope that the genocide designation will raise international consciousness, end the scandal of silence, and create the preconditions for the protection and reintegration of these ancient faith communities into their ancestral homelands.”

Sen. Ben Sasse (R-Neb.), who introduced a similar resolution in the Senate this week, also praised Thursday’s declaration.

“Telling the truth and condemning genocide against those who seek to worship or not worship as they see fit is a small but important step to recovering a coherent American foreign policy,” he said in a statement. “This decision does not end the atrocities, but it does name them.”

In his statement , Kerry said a U.S.-led coalition that has been conducting airstrikes against Islamic State targets in Iraq and Syria has helped push the militants out of 40 percent of the territory they controlled in Iraq and 20 percent of their territory in Syria.

Although it is “impossible to develop a fully detailed and comprehensive picture of all that Daesh is doing,” Kerry said, the U.S. review highlighted a number of cases of atrocities. For example, he said, Islamic State fighters killed hundreds of Yazidis in their village in northern Iraq,trapped others on nearby Mount Sinjar and “enslaved thousands of Yazidi women and girls,” raping many of them.

He said the Islamic State has summarily executed Christians in Mosul, the militants’ main stronghold in northern Iraq, and in Libya, where the group has been making inroads.

Kerry also cited the massacre of hundreds of Shiite Turkmens, an ethnic and religious minority, and the systematic destruction of antiquities, churches, monasteries and other elements of the cultural heritage of ancient communities.

Recounting the story of a 14-year-old boy who was recruited by the Islamic State and sent to carry out a suicide bombing against Shiites, Kerry quoted the group as having declared that “it is a duty imposed upon us to kill them . . . and to cleanse the land of their filth.”

Michelle Boorstein contributed to this report.