(CNN) -

Ahmed Godane, the leader of the Somali militant group Al-Shabaab, was killed this week in a U.S. military operation, the Pentagon said Friday.

"The U.S. military undertook operations against Godane on Sept. 1, which led to his death. Removing Godane from the battlefield is a major symbolic and operational loss to Al-Shabaab," said Pentagon press secretary Rear Adm. John Kirby.

On Monday, U.S. military conducted a strike in the African country targeting Godane, who had pledged allegiance to al Qaeda. He headed Al-Shabaab as it terrorized East Africa, killing Somali officials, aid workers and others in a spate of suicide bombings. Godane allegedly was behind 2013's deadly siege of a Nairobi, Kenya, shopping mall.

Before this week's strike, the U.S. military was tipped off to what Kirby called "actionable intelligence ... strong enough" to suggest Godane's whereabouts.

In response, U.S. commandos flew -- aided by drones -- into an area south of the Somali capital, Mogadishu, around 6:20 p.m. (11:20 a.m. ET) Monday.

Abdikadir Mohamed Nur Sidii, governor of Somalia's Lower Shabelle region, characterized the attack near the port city of Barawe as so ferocious "it jolted the entire region."

Sidii said, "I never heard such a huge and deafening blast as the result of the airstrike."

Earlier this week, Kirby didn't elaborate on how much firepower was involved, beyond the use of Hellfire and laser-guided missiles. Somali intelligence officials counted at least four such missiles.

After the attack, an Al-Shababb Twitter account said one person was killed but asserted it wasn't Godane. "'Ahmed Abdi Godane' is alive and doing fine," the tweet said, calling itself an "official mujahedin account" in the Islamic land of Somalia.

At the time, CNN was unable to verify the authenticity of that claim on Twitter.

The man behind Al-Shabaab

Godane, who was also known as Mukhtar Abu Zubayr, became the leader of Al-Shabaab in 2008.

Traditionally, Al-Shabaab focused on bringing Islamic rule to Somalia, attracting dozens of ethnic Somalis -- and a few Westerners -- from the United States and Europe.

But last year Godane seemed to be refocusing the group on terrorist attacks beyond Somalia -- against East African states supporting the Somali government, especially Uganda and Kenya, and against Western interests in East Africa.

The September 2013 Westgate Mall attack in Kenya's capital was Al-Shabaab's most audacious, but the massacre that left 67 people dead wasn't the group's first strike outside Somalia. In 2010, Al-Shabaab carried out suicide bombings in the Ugandan capital, Kampala, in which more than 70 people were killed.

Still, the Westgate siege demonstrated Godane's desire to align his group more closely with al Qaeda. In a taped message afterward, he noted the attack took place "just 10 days after the anniversary date of the blessed 9/11 operations."

Under Godane, Al-Shabaab became a formal ally of al Qaeda. The move led to dissent in the group, which Godane dealt with ruthlessly, using his control of Al-Shabaab's intelligence wing. The American jihadist Omar Hammami was reportedly killed in September 2013 after criticizing Godane's leadership and his treatment of foreign fighters.

Godane was said to be 37 years old, and was originally from Somaliland in northern Somalia. He was slim to the point of wispy, as seen in the few photographs of him, and preferred recording audio messages to appearing in public.

A former Somali prime minister, Omar Abdirashid Ali Sharmarke, once described Godane as the cleverest of Al-Shabaab's leaders.

The U.S. government's Rewards for Justice program listed him under another alias, Ahmed Abdi Aw-Mohamed, and offered up to $7 million last year for information leading to his location.