ISLAMABAD/KABUL, June 1 (Reuters) – Al Qaeda’s operations chief and third-in-command, Sheikh Sai’d al-Masri, is believed to have been killed in a U.S. missile strike in Pakistan last month, U.S. and Pakistani officials said.

Al Qaeda has confirmed the death of Masri, who is also known as Mustafa Abu al-Yazid, in a statement on an Islamist website but gave no details.

U.S. and Pakistani intelligence officials believe Masri was killed, along with members of his family, in a strike by a pilotless CIA-operated drone in tribal areas along the border with Afghanistan in late May.

Following are some facts about him.

WHO IS SAI’D AL-MASRI?

He was born on Dec. 17, 1955, in Egypt and became a militant Islamist in his youth, spending three years in prison.

Masri was a founding member of al Qaeda number two Ayman al-Zawahiri’s branch of the Egyptian Islamic Jihad, one of the original groups that merged to form al Qaeda. Following the assassination of Egyptian President Anwar Sadat in 1981, Masri was implicated in the killing along with Zawahiri and others, and they spent time in jail together.

He left Egypt for Afghanistan in 1988 and was subsequently convicted in absentia for militant offences in several trials in Egypt, and was sentenced to both life imprisonment and death.

Masri accompanied Osama bin Laden from Afghanistan to Sudan in 1991. While there he served as an accountant for bin Laden’s Sudan-based businesses before returning to Afghanistan with bin Laden in 1996.

Masri is reported to have supplied funding for Mohammed Atta, the leader of the Sept. 11, 2001, attacks on the United States.

WHAT WAS HIS ROLE IN AL QAEDA?

Masri was one of al Qaeda’s most important and trusted leaders. He was al Qaeda’s leader in Afghanistan and in what the group refers to as the Khorasan, a region encompassing large areas of Afghanistan, Pakistan, Uzbekistan, Tajikistan and Iran.

The Khorasan is considered by jihadists to be the place where they will inflict the first defeat against their enemies in the Muslim version of Armageddon.

He also served as a top propagandist for al Qaeda and the Taliban. Bespectacled Masri, wearing a white turban, often appeared on propaganda tapes with senior Taliban leaders.

As one of the founding members of al Qaeda in the late 1980s, Masri was a close associate of bin Laden. He also was a member of al Qaeda’s Shura Council, its core leadership forum.

Among Islamist groups, Masri was reputed to be a diplomatic personality who had good relations among local militants in Afghanistan and Pakistan. His appointment as the leader of Afghan operations in May 2007 was seen by experts as a bid by al Qaeda to boost its ties to local insurgents.

The U.S. September 11 Commission described Masri as the network’s “chief financial manager”. He was also believed to have opposed the September 11 attacks prior to their execution, but he remained loyal to al Qaeda and bin Laden.

HOW SIGNIFICANT IS HIS DEATH?

Security experts say his death would be a blow. Al Qaeda has suffered a steady erosion of its leadership and ability to mount attacks since the United States stepped up its campaign of missile strikes by unmanned aircraft in Pakistan’s tribal region.

His death could also hamper al Qaeda’s ability to raise and distribute funds because he was in charge of the group’s “bayt ul mal”, or treasury. Because of his seniority he will be difficult to replace, security experts say.

Masri, which means “the Egyptian”, was the most senior al Qaeda leader killed in Afghanistan since military commander Mohammad Atef died in a U.S. air strike on his home in Kabul in November 2001.

He was also the highest ranking al Qaeda operative to have been killed in Pakistan’s tribal belt this year. In 2008, Pakistani security officials had said he was killed in military clashes in the northwestern Bajaur tribal region but that was later proved incorrect.

WHAT DID HE SAY WHEN HE WAS ALIVE?

One of the few recognisable faces of al Qaeda, Masri issued warnings and threats to countries and leaders the group considers itself waging holy war, or jihad, against.

In an interview aired on Al Jazeera television in June 2009, Masri said al Qaeda would use Pakistan’s nuclear weapons in its fight against the United States if it were in a position to do so. When asked about the whereabouts of bin Laden and Zawahiri, he said they were “safe”.

In a video seen by Reuters in 2009, Masri warned India of more attacks like the 2008 operation in its financial capital Mumbai and said India’s economic interests would be targeted if it retaliated against Pakistan.

Masri also told Pakistan’s Geo television in an interview aired in 2008 that a suicide bomber who attacked the Danish embassy in Islamabad that year came from the Muslim holy city of Mecca in Saudi Arabia.

In a June 2009 audio message, Masri said militants were short of food, weapons and other supplies and appealed for funding. In a January 2010 message, he praised a Dec. 30, 2009, attack at a U.S. base in Afghanistan in which a Jordanian double agent turned suicide bomber killed seven CIA officers.

(Additional reporting by William Maclean in LONDON; Editing by Chris Allbritton and Miral Fahmy) (For full coverage of Pakistan and Afghanistan, click on [ID:nAFPAK] (For more Reuters coverage of Afghanistan and Pakistan, see: here)