Two people were killed and over a dozen injured in a shooting outside a beer garden in Austin, Texas, in an incident the FBI says may be related to terrorism.

The suspect has been identified as Ndiaga Diagne, a naturalised American citizen born in Senegal, according to the BBC's US partner CBS News and other US media.

After responding to calls of an active shooter at around 02:00 local time (08:00 GMT) on Sunday near Buford's bar in the southern US state's capital, police said they shot and killed the suspect, bringing the death toll to three.

Police have not offered a motive and have not officially identified Diagne. Of the survivors, 14 were taken to hospital, three in a critical condition.

Two sources familiar with the investigation told CBS News that the gunman was wearing a sweatshirt with the words "Property of Allah".

CBS was also told by an official with knowledge of the investigation that officers who searched the gunman's home found an Iranian flag and pictures of Iranian leaders. The attack came on the weekend that the US and its ally Israel launched multiple strikes on Iran, killing Supreme Leader Ayatollah Ali Khamenei.

Austin Police Chief Lisa Davis said officers who were on patrol in the more popular, crowded bar district known as East Sixth Street quickly responded to reports of a man with a gun at Buford's, located farther down on West Sixth Street.

She said a man in a large SUV driving by Buford's put on the vehicle's hazard lights, rolled down his window and fired a pistol, striking people on the patio and pavement outside the bar.

He parked the vehicle nearby, got out with a rifle and started walking back towards the bar, according to Davis. Three police officers confronted the suspect at an intersection, and shot and killed him.

The SUV was searched and was not carrying explosives, officials said.

However, Acting Special Agent in Charge Alex Doran, from the FBI's San Antonio office, said there were indications in the SUV and on the suspect that suggested a "nexus to terrorism".

But Doran said the investigation was in its early stages and he was "not prepared to release those details".

"We are committed to seeing this process through to the very end," he said.

Kelson Lee, 25, was within earshot when gunfire erupted at Buford's. He walked inside to look for a friend, according to the Austin Current.

"I see about seven to eight bodies on the floor," Lee told the local news outlet. "No-one should ever have to see that.

"I kind of blacked out, froze up. I felt kind of helpless because I wanted to help people."

Of the 14 people taken to the hospital, three were in a critical condition Austin-Travis County Emergency Management Services head Rob Luckritz said.

US President Donald Trump has been notified of the shooting, White House Press Secretary Karoline Leavitt said.

Republican Senator Ted Cruz, who represents Texas, condemned the deadly attack in a post on social media.

"What happened early this morning in Austin was a senseless act of violence. My team and I are co-ordinating with local, state, and federal authorities," he wrote.

"I'm grateful for the heroic and quick response from law enforcement."

Davis said that because of increased police and emergency resources in the entertainment area over the weekend, they were able to "rapidly" respond to the scene.

Austin Mayor Kirk Watson also praised the response by police and rescuers, which officials said took 57 seconds. "I'm very thankful for the speed," he said. "They definitely saved lives."

Texas Governor Greg Abbott vowed that "this act of violence will not define us, nor will it shake the resolve of Texans".

Austin is home to both the Texas capitol and one of the state's largest public universities, the University of Texas, which is near the city's downtown, less than two miles (3.2km) from Buford's.

East Sixth Street and West Sixth Street are popular destinations for the roughly 55,000 students, who frequent the area most weekends.

Jim Davis, president of the University of Texas, said in a statement: "Our prayers are with the victims and all those impacted, including members of our Longhorn family, and my heart goes out to their families, friends, classmates, professors, and loved ones."