WASHINGTON -- U.S. airstrikes earlier this week killed the leader of the al-Shabab terrorist group in Somalia, the Pentagon said Friday. President Barack Obama said the death of Ahmed Abdi Godane demonstrated U.S. counterterrorism resolve and was an example of his deliberate approach to dismantling al-Qaida affiliated groups.

The Pentagon's press secretary, Rear Adm. John Kirby, announced the death in a brief written statement. It took the Pentagon four days to conclusively determine that Godane had not survived Monday's airstrikes.

Al-Shabab has not publicly confirmed Godane's death.

Obama, speaking at the conclusion of a NATO summit in Newport, Wales, told reporters the success against al-Shabab should leave no doubt about his determination to degrade and eventually destroy the Islamic State group in Iraq and Syria. He faces mounting pressure to take more aggressive military action against the Islamic State, which evolved from an al-Qaida affiliate that sprouted in Iraq in 2004.

"We have been very systematic and methodical in going after these kinds of organizations" that threaten U.S. personnel and the homeland, Obama said. "That deliberation allows us to do it right, but have no doubt: We will continue to do what is necessary to protect the American people."

U.S. officials had said after the strike on Monday that U.S. special operations forces using manned and drone aircraft had destroyed an encampment and a vehicle using several Hellfire missiles and laser-guided munitions. But they did not confirm that Godane had been killed until Friday.

The State Department declared al-Shabab a terrorist organization in February 2008. The implications of the group's loss of Godane are unclear.

"The individual who takes his place will live in fear," said Army Col. Steven Warren, a Pentagon spokesman.

Because Godane had weakened and effectively dismantled the al-Shabab council of leaders known as the shura, a meeting of regional commanders will have to take place to pick his successor, said Matt Bryden, the head of Sahan Research in Nairobi, Kenya. Bryden predicted the meeting will be difficult and dangerous to organize.

Terrorism analyst J.M. Berger said there is significant support in al-Shabab's rank and file to pledge allegiance to the Islamic State group that Obama also has pledged to degrade and destroy. Berger predicted a significant splintering between al-Shabab's domestically focused insurgents and internationally aspiring terrorists.

Kirby said on Tuesday, before the Pentagon was certain that Godane had died, that the U.S. strike was conducted south of Mogadishu and that it had destroyed the vehicle that was targeted. He noted that in September 2013, Godone had publicly claimed al-Shabab was responsible for the Westgate Mall attack in Nairobi, Kenya, that killed at least 67 people.

"Under the leadership of Godane, al-Shabab has claimed responsibility for many bombings, including suicide attacks in Mogadishu and in central and northern Somalia, typically targeting officials and perceived allies of the federal government of Somalia, as well as the former transitional federal government of Somali," Kirby said Tuesday.