A gunman opened fire at a US Navy base in Corpus Christi, Texas, wounding a sailor, before being killed at the scene of the incident that authorities said was linked to terrorism.
"We have concluded that the incident (Thursday morning local time) at Corpus Christi Naval Air Force Base is linked to terrorism," said FBI spokeswoman Lea Greaves.
She added that the investigators are looking for another person who may be related to the attacker and is moving at large in the area.
American media said that the attacker was named as Adam Salim Al-Sahili, who is a US-born Syrian resident.
CNN quoted sources familiar with the preliminary investigations as saying that the attacker was a supporter of Salafi jihadism.
Meanwhile, the US Navy announced that the sailor who was wounded in the attack - a member of the al-Qaeda security force - was in good condition and was discharged from hospital.
Last December, a Saudi gunman killed three American sailors in an attack at the Pensacola Naval Base in Florida, days after an American sailor shot three civilians at Pearl Harbor Military Base in Hawaii, killing two of them and then committing suicide.