US President Donald Trump said Monday that US special forces had captured a man linked to the 2012 attack on the American mission in the Libyan city of Benghazi.

"Yesterday, on my orders, United States forces captured Mustafa al-Imam in Libya," Trump said in a statement, which came as the White House was rocked by the indictment of three campaign aides.

Trump said "al-Imam will face justice in the United States for his alleged role in the September 11, 2012 attacks in Benghazi."

Attorney General Jeff Sessions confirmed that the suspect "will face justice in federal court for his role in the attack."

An alleged mastermind of the attack, 46-year-old Ahmed Abu Khattala, is already on trial in the United States, accused of being a commander of the Ansar al-Sharia militia.

The attack killed US ambassador Chris Stevens as well as three other American personnel and became emblematic of conservative opposition to then secretary of state Hillary Clinton.

Several congressional investigations were launched, along with a State Department security review, into both the handling of the attack and how it was described in the media.

Clinton was never convincingly tagged with wrong-doing or negligence, but the issue haunted her failed 2016 presidential campaign and may have contributed to Trump's victory.

US Secretary of State Rex Tillerson welcomed Trump's announcement.

"I am deeply grateful to the US military, law enforcement, and intelligence community for their efforts to bring to justice the perpetrators of the September 11, 2012 terrorist attacks," he said.

Tillerson said he had spoken to some of the relatives of those killed in the raid "to underscore the US government's unwavering support."

- Choking on smoke -

On September 11, 2012 -- the anniversary of the 2001 Al-Qaeda attacks on New York and Washington -- Islamist militants launched a surprise attack on a US diplomatic compound in Benghazi.

The eastern city had been a hotbed of support for the rebels who the year previously, backed by NATO bombing runs, had overthrown dictator Moamer Kadhafi.

But since the fall of the regime, like many areas of Libya, it had fallen prey to faction fighting among rival militias -- including some inspired by global jihadist groups.

Then president Barack Obama's government was criticized for, in some initial reactions, ascribing the attack to regional popular anger over a US-produced, amateur anti-Islam film.

But it was subsequently concluded that it was a coordinated militant operation.

Ambassador Stevens and Sean Smith, a State Department technician, died of smoke inhalation as armed men attacked and set fire to a building in the diplomatic compound.

The group later fired mortar rounds at a building used by the CIA, killing Glen Doherty and Tyrone Woods, two former members of the Navy SEALs working as contractors.

Trump's statement did not go into detail as to how the latest suspect, Al-Imam, was captured.

But Abu Khattala was captured in 2014 when US special forces carried out a commando raid based on intelligence provided by a friend who received a $7 million reward from the US government.

Abu Khattala was taken to a US Navy ship where he was first subjected to a secret, classified interrogation before being questioned by FBI agents who informed him of his legal rights.

Defense attorneys have since claimed that his 13-day voyage to the United States was dragged out unnecessarily to prevent him from having proper legal counsel. Prosecutors deny this.

- Hunt for justice -

Trump suggested that even the second arrest had not brought an end to the US hunt for justice.

"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 said.

"Our memory is deep and our reach is long, and we will not rest in our efforts to find and bring the perpetrators of the heinous attacks in Benghazi to justice."

He restated US support for the UN-backed reconciliation process in Libya and urged its citizens to supports efforts to build a unified government and military.

Source: AFP