The strikes, which took place over the past two days, occurred in Jilib, about 200 miles southwest of Mogadishu.
"U.S. forces work closely with Somali military forces against al-Shabaab in Somalia to degrade the al-Qaeda affiliate's ability to recruit, train, and plot external terror attacks throughout the region and in the United States," U.S. Africa Command said in a statement on Thursday.
According to a U.S. official, one strike against the group was conducted in self-defense after a group of armed al-Shabaab fighters posed an imminent threat to Somali-led and U.S. forces, leading the U.S. to conduct the strike to neutralize the threat.
Before the new authorization was granted, the U.S. military could only carry out defensive airstrikes against al-Shabaab in situations where Somali troops and their U.S. advisers came under fire.
These air strikes bring the total number directed under the new, offensive policy to seven.
Last week, the U.S. confirmed two additional offensive strikes against al-Shabaab fighters. Three other offensive strikes were carried out in June and July.
"Al-Shabaab has pledged allegiance to al-Qaeda and is dedicated to providing safe haven for terrorists," U.S. Africa Command said in its statement. "We continue to work in coordination with our Somali partners and allies to systematically dismantle al-Shabaab and help achieve stability and security throughout the region."
ABC News' Luis Martinez contributed to this report.