Maj. Emmanuel Chirchir, a Kenyan military spokesman, told reporters Friday the four suspects were "the terrorists" who led the shooting spree that took the lives of at least 67 people.
Chirchir said the four included one Kenyan of Arab origin as well as operatives from Sudan and Somalia, the home base of al-Shabaab.
The suspects were identified as Abu Baara al-Sudani, Omar Nabhan, Khattab al-Kene and Umayr. It was not known whether they were at large or had been killed in the mall attack.
The announcement was made at the same time police said they suspected four or five gunmen had carried out the raid rather than the 10-15 originally believed to be involved, the BBC said.
The United States has been considering its options in response to the attack. Voice of America said Saturday the most likely option was assisting Kenya in going after al-Shabaab in neighboring Somalia.
A defense analyst said at a congressional hearing a key would be convincing Kenya not to overreact and launch strikes into Somalia, VOA said.
A team of U.S. Navy SEALs carried out a predawn commando raid on one of al-Shabaab's hideouts on the Somali coast overnight, a U.S. official told The Washington Post Saturday. The source told the newspaper the SEALs were unable to capture the al-Shabaab leader they were targeting.