A US Africa Command spokesperson said Friday's airstrike had no link to the anniversary.
The airstrike was launched in coordination with the Somalian government Friday near the Harardere community in Mudug province in central Somalia.
United States military officials have expressed concern that the group is again growing - even after losing much of its territory in Somalia in recent years and being targeted by U.S. drone strikes. Washington says its attacks target militants groups.
It was the largest USA air strike since a November 2017 attack, which killed about 100 al-Shabab fighters.
The strike came after a recent spate of attacks that Al-Shabab has conducted against Somali security forces and their USA advisers across the country. The U.S. on Tuesday said about 60 extremists were killed.
AFRICOM said that they are committed to preventing al-Shabaab from taking advantage of safe havens from which they can build capacity and attack the people of Somalia.
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The officials spoke on condition of anonymity because they were not authorised to speak to reporters.
Under President Trump, the United States military has increased its involvement in the fight against al-Shabaab, the deadliest Islamic extremist group in sub-Saharan Africa.
Al-Shabaab, which seeks to establish an Islamic state in Somalia, continues to hold parts of the country's south and central regions after being chased out of Mogadishu several years ago.
The US military's activities in Somalia have been under scrutiny in recent months after US special forces in May were accused of complicity in a botched raid by Somali troops that left five civilians dead.
The US military has carried out more than two dozen air strikes, including drone strikes, this year against the al-Qaeda-linked al-Shabab.