Al-Shabaab claimed responsibility for two attacks July 11 in Kampala that killed more than 70 people during celebrations for the World Cup soccer tournament. Al-Qaida reacted positively to the attack.
A senior U.S. intelligence official told the online Long War Journal that al-Qaida called on the Somali group to be more reserved, however.
"Al-Qaida is pleased with the double suicide attack in Uganda, but suggested al-Shabaab reserve future strikes at U.S. interests in the region," the official said on condition of anonymity.
U.S. Attorney General Eric Holder announced Aug. 4 that the Justice Department charged 14 men with providing material support for al-Shabaab, a designated terrorist group with ties to al-Qaida.
Twelve of the 14 suspects named by Holder aren't in custody and are believed to be overseas, possibly in Somalia, the Justice Department said.
In July, the Justice Department announced the arrest of Zachary Adam Chesser, 20, on charges of providing material support to al-Shabaab.
Chesser reportedly confessed to federal agents he tried twice to join al-Shabaab.
The intelligence official said al-Qaida was worried that overexposure may be attracting too much attention for al-Shabaab.
"Al-Qaida's top leadership has instructed al-Shabaab to maintain a low profile on al-Qaida links," the official said.