The gunman who killed 26 people and wounded about 20 others in an attack on a small church in Texas was dressed in black tactical-style gear and a ballistic vest and was armed with an assault rifle, police have said.

The attacker, identified in US media as Devin Patrick Kelley, used a Ruger AR rifle and also carried a handgun, Wilson County Sheriff Joe D Tackitt Jr said.

Several weapons were left inside the vehicle he was found dead inside after leaving the attack, Freeman Martin, a regional director of the Texas Department of Safety, said.

(Facebook)

Investigators were looking at social media posts Kelley made in the days before the attack, including one appearing to show an AR-15 rifle with the caption "She's a bad b****."

The Ruger AR-556 is a variant of the popular AR-15 rifle, known for being highly customisable.

The model which appeared in Kelley's Facebook post has a recommended retail price of $849 (£647).

The magazine-fed, gas-operated, semi-automatic rifle is based on the military's M-16 rifle.

However, unlike the M-16, the AR-15 does not have burst or automatic fire modes. Each pull of the trigger fires one shot.

But some modifications, such as the bump-stock used in the Las Vegas shooting, can significantly increase the rate-of-fire.

It is unknown whether the Texas church shooter had modified his rifle.

Texas church shooting Show all 9 1 /9 Texas church shooting Texas church shooting The site of the mass shooting at First Baptist Church in Sutherland Springs, Texas Reuters Texas church shooting First responders are at the scene of shooting at the First Baptist Church Reuters Texas church shooting Enrique and Gabby Garcia watch investigators at the scene of the mass shooting AP Texas church shooting Law enforcement officials investigate the scene at the First Baptist Church in Sutherland Springs, Texas Reuters Texas church shooting Carrie Matula embraces a woman after a fatal shooting at the First Baptist Church in Sutherland Springs Associated Press Texas church shooting Law enforcement officials gather near the First Baptist Church Getty Images Texas church shooting Community members come together for a candlelight vigil for the victims of the deadly church shooting in Sutherland Springs Laura Skelding/AP Texas church shooting Mourners participate in the candlelight vigil held for the victims Jay Janner/Austin American-Statesman via AP Texas church shooting A vehicle is hauled onto a flatbed truck where the suspect in a deadly church shooting was found dead in Guadalupe County William Luther/Austin American-Statesman via AP

Typically, the AR-15 is loaded with a 30-round magazine, but larger magazines with a capacity for 75 to 100 rounds are also available.

There is no limit in Texas to the amount of ammo rifles can be loaded with.

In Texas, AR-15 rifles can be purchased without a permit or waiting period.

The weapon does not need to be registered and people are allowed to openly carry them without a permit.

While a license is required to carry a handgun in Texas, it is not required for a rifle.

Trump says Texas shooting 'not a guns problem'

Kelley received a bad-conduct discharge from the Air Force for allegedly assaulting his spouse and child. He was sentenced to 12 months' confinement in 2012 after a court-martial.

Donald Trump said the mass shooting wasn't "a guns situation" and was due to a "mental health problem."