Special operations forces on Sunday captured a top militant suspected of helping lead the deadly 2012 attacks against a U.S. diplomatic compound in Benghazi, Libya, the White House announced Monday.

"Yesterday, on my orders, United States forces captured Mustafa al-Imam in Libya," President Trump said in a statement.

U.S. commandos grabbed al-Imam during a joint mission that was approved by both Trump and the Libyan government, officials told The Associated Press shortly before the administration made a formal announcement.

The militant, who is set to be transported to the U.S. for federal prosecution, is seen as a key player in the assault against the consulate annex that resulted in the deaths of Ambassador Christopher Stevens and three other Americans.

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"The United States will continue to support our Libyan partners to ensure that [the Islamic State in Iraq and Syria] and other terrorist groups do not use Libya as a safe haven for attacks against United States citizens or interests, Libyans, and others," Trump's statement said, stressing that he plans to pursue the other "perpetrators of the heinous attacks."

"To the families of these fallen heroes: I want you to know that your loved ones are not forgotten, and they will never be forgotten," he added.

Secretary of State Rex Tillerson Rex Wayne TillersonGary Cohn: 'I haven't made up my mind' on vote for president in November Kushner says 'Alice in Wonderland' describes Trump presidency: Woodward book Conspicuous by their absence from the Republican Convention MORE on Monday echoed that they will continue to track down those responsible for the attack.

"The Department of State family continues to mourn the loss of Ambassador Chris Stevens, Glen Doherty, Sean Smith, and Tyrone Woods, and we will spare no effort to ensure that justice is served for these dedicated Americans and public servants," Tillerson said in a statement.

Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE called the attack a "barbaric crime" and said the arrest is "a major step forward in our ongoing investigation."

Al-Imam, who could have operated under different aliases, was caught on video at one of the two Benghazi sites of the attacks, an administration official told CNN.

Republicans have hammered the Obama administration, in particular then-Secretary of State Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE, over the response to the deadly Benghazi attack.

Multiple GOP congressional panels led probes into the Sept. 11, 2012, attack, frequently complaining about a lack of cooperation from the Obama White House

Trump weighed in with his own criticism at the time, suggesting the administration misled Americans on the details of the deadly attacks.

"Benghazi is bigger than Watergate. Don’t let Obama get away with allowing Americans to die. Kick him out of office tomorrow," Trump tweeted in November 2012.

Initially, the Obama administration said it was a spontaneous attack sparked by anger over an anti-Muslim film. Later, officials said it was a planned attack.

—Updated at 5:04 p.m.