Authorities in Egypt have detained the alleged mastermind of an Egyptian terror network whose members participated in the September 11 attack on a US consulate in Libya that killed US Ambassador Chris Stevens and three other Americans, the Wall Street Journal reported Friday.

Muhammad Jamal Abu Ahmad, a former member of the Egyptian Islamic Jihad, was considered one of the most “menacing operatives to emerge in the region in the wake of the Arab Spring,” according to Western counterterrorism officials, the news site added.

He had operated in Egypt after the fall of former Egyptian president Hosni Mubarak and then traveled to assist Jihadi fighters in Libya, Israel Radio reported. He also reportedly received assistance from al-Qaeda in Yemen.

A US official confirmed to AFP late Friday that Abu Ahmad had been arrested but did not provide further details.

Also on Friday, Sen. John Kerry said US Secretary of State Hillary Clinton has agreed to testify before the Senate Foreign Relations Committee about an independent report on the Benghazi attack.

In a letter Friday to the panel’s members, Kerry indicated that the report from the accountability review board headed by retired diplomat Thomas Pickering is imminent. The Massachusetts Democrat and committee chairman says he’s asked that Pickering and retired Adm. Mike Mullen appear before the committee before Clinton. Mullen, the former chairman of the Joint Chiefs of Staff, is a member of the review board.

Clinton has also agreed to testify before the House Foreign Affairs Committee.