Secretary of State John Kerry declared Thursday that the Islamic State is committing genocide against Christians and other minorities in the Middle East, after facing heavy pressure from lawmakers and rights groups to make the rare designation.

“In my judgment, Daesh is responsible for genocide against groups in territory under its control, including Yazidis, Christians and Shia Muslims,” Kerry said at the State Department, referring to the terror group by an adapted acronym of its Arabic name.

He accused ISIS of “crimes against humanity” and "ethnic cleansing."

The announcement was a surprise, at least in terms of the timing. A day earlier, a State Department spokesman said they would miss a congressionally mandated March 17 deadline to make a decision. Yet as the department took heat from lawmakers for the expected delay, the department confirmed Thursday morning that Kerry had reached the decision that Christians, Yazidis and Shiite groups are victims of genocide.

It comes after the House this week passed a nonbinding resolution by a 393-0 vote condemning ISIS atrocities as genocide.

Kerry's finding will not obligate the United States to take additional action against ISIS militants and does not prejudge any prosecution against its members, said U.S. officials.

Kerry, though, urged others to join in holding the group “accountable”; he called for an “independent investigation” as well as a court or tribunal to take action to that end.

Saying the terror network is “genocidal” in what it says, believes and does, Kerry recited a litany of documented atrocities including the execution of Christians in Iraq “solely because of their faith” and of Yazidis.

Lawmakers and others who have advocated for the finding had sharply criticized the department's disclosure Wednesday that the deadline would be missed. The officials said Kerry concluded his review just hours after that announcement and that the criticism had not affected his decision.

“Secretary Kerry is finally making the right call,” House Foreign Affairs Committee Chairman Ed Royce, R-Calif., said in a statement after the announcement Thursday. He added that “President Obama should step up and lay out the broad, overarching plan that’s needed to actually defeat and destroy ISIS. This administration’s long pattern of paralysis and ineffectiveness in combating these radical Islamist terrorists is unacceptable.”

The determination marks only the second time a U.S. administration has declared that a genocide was being committed during an ongoing conflict.

The first was in 2004, when then-Secretary of State Colin Powell determined that atrocities in Sudan's Darfur region constituted genocide. Powell reached that determination amid much lobbying from human rights groups, but only after State Department lawyers advised him that it would not -- contrary to legal advice offered to previous administrations -- obligate the United States to act to stop it.

In that case, the lawyers decided that the 1948 U.N. Convention against genocide did not require countries to prevent genocide from taking place outside their territory. Powell instead called for the U.N. Security Council to appoint a commission to investigate and take appropriate legal action if it agreed with the genocide determination.

The officials said Kerry's determination followed a similar finding by department lawyers.

Although the United States is involved in military strikes against ISIS and has helped prevent some incidents of ethnic cleansing, notably of Yazidis, some advocates argue that a genocide determination would require additional U.S. action.

In making his decision, Kerry weighed whether the militants' targeting of Christians and other minorities meets the definition of genocide, according to the U.N. Convention: "acts committed with intent to destroy, in whole or in part, a national, ethnic, racial or religious group."

His determination, however, does not carry the legal implication of a verdict of guilt or conviction on genocide charges, the officials said. Such decisions will be left to international or other tribunals.

In a bid to push the review process, several groups released reports last week documenting what they said is clear evidence that the legal standard has been met.

The Knights of Columbus and In Defense of Christians, which had applauded Monday's House resolution, said they hoped the delay would ensure that Kerry makes the determination.

"There is only one legal term for this, and that is genocide," said Knights of Columbus chief Carl Anderson.

The groups' 280-page report identified by name more than 1,100 Christians who they said had been killed by ISIS. It detailed numerous instances of people kidnapped, raped, sold into slavery and driven from their homes, along with the destruction of churches.

The Associated Press contributed to this report.