SUTHERLAND SPRINGS, Texas (TNS) — At least 26 people were shot and killed Sunday when a 26-year-old gunman dressed in black opened fire at a Baptist church in a small town near San Antonio.

An additional 20 people were injured in the attack, which happened as a church service was underway at First Baptist Church in the town of Sutherland Springs, police said.

Freeman Martin, regional director of the Texas Department of Public Service, said the suspect, dressed all in black and wearing a tactical vest, initially began firing with an AR-15-style Ruger rifle outside the church at about 11:20 a.m., then entered the church and continued firing.

After the gunman left the church, a local citizen drew his own weapon and engaged the suspect, who dropped his weapon. The unidentified citizen then pursued the suspect by car into an adjacent county, where the suspect ran off the road and was later found dead in his vehicle with multiple weapons inside, Martin said.

"At this time, we don't know if it was a self-inflicted wound or if he was shot by our local resident," Martin said. The citizen who confronted the gunman was unhurt.

Sunday's mass shooting was the deadliest in the modern history of Texas, surpassing a 1991 massacre in Killeen that left 23 dead. The top five deadliest shootings in modern American history have all come in the last 10 years, with two of them in the past six weeks: the Oct. 1 shootings in Las Vegas, which killed 58, and now, the shooting in Sutherland Springs.

President Donald Trump, who has been briefed on the attack on his trip to Asia, called it a "horrific shooting" in a "place of sacred worship."

In a time of crisis, he said, "Americans will do what we do best: We pull together and join hands and lock arms and through the tears and sadness we stand strong."

Wilson County Sheriff Joe Tackett appealed for understanding during the crisis. "We need your support," he said at a news conference. "And media, don't blow it out there that it should have never happened, because it does happen, and we sincerely feel sorry for all the people who are involved."

According to a sketchy police account of the incident, two people were killed outside the church, 23 people were killed inside and one person died after being taken to the hospital. The victims' ages ranged from 5 to 72 years old.

The deaths were a devastating shock to a community with only a few hundred residents. "I know at least five people who were killed" said Chris Taylor, 59, who owns a gas station two blocks from the church.

News of the shooting spread quickly around the small town.

"We were on top of the barn, fixing the roof, when we heard the shots," said neighbor Renee Shedelbower, 54, who lives a mile from the church. "We didn't think anything of it because deer hunting season started yesterday, but when we heard the sirens we knew something was wrong."

Local police declined to identify the suspect, but a Texas congressman and another law enforcement source identified him as Devin P. Kelley, 26, a resident of Comal County, Texas.

A Facebook profile under the gunman's name featured a photo of an AR-15-style semi-automatic rifle. In recent months, Kelley was adding strangers as friends on Facebook from "within 20 minutes" of the Sutherland Springs area and starting Facebook fights with them, according to area resident Johnathan Castillo.

Castillo accepted Kelley's friend request a couple of months ago, thinking that maybe he or his friends had met Kelley but hadn't remembered him. But Kelley soon proved to be troublesome.

"A lot of people were deleting him" for "starting drama" on Facebook, including sending insulting Facebook messages, Castillo said.

"It's like he went looking for it, you know what I mean?" Castillo said. "You can tell people who are defending their opinions, versus someone who's looking to start something."

Castillo said he was angry with the gunman, noting the picture of the rifle on Kelley's Facebook page, "making the rest of us who actually hunt look bad."

A LinkedIn profile under Kelley's name featured Kelley in a photo with a baby and said that he was a "management consulting professional" from the San Antonio area who was in the U.S. Air Force from 2009 to 2013. "I am a hard working dedicated person," the profile said. "I live by the core values on which the Air Force go by."

The profile said Kelley taught "children ages 4-6 at vocational bible schools helping their minds grow and prosper" at the Kingsville First Baptist Church.

His interests in LinkedIn included "Animal Welfare," "Children," "Civil Rights and Social Action" and "Human Rights."

Investigators have not given any possible motive for the attack.

"The details of this horrific act are still under investigation," Texas Gov. Greg Abbott said in a statement before he headed to join local, state and federal officials at the scene. "I want to thank law enforcement for their response and ask that all Texans pray for the Sutherland Springs community during this time of mourning and loss."

U.S. Rep. Henry Cuellar, D-Texas, said the dead included a pregnant woman and children, based on the congressman's briefing with local law enforcement authorities.

The dead also included the daughter of the church's pastor, Frank Pomeroy, who was in Oklahoma when the shooting happened. Annabelle Renee Pomeroy was "one very beautiful, special child," Pomeroy told ABC News, adding that the dead were all close friends of his.

At least 10 victims, including four children, were being treated at the University Health System in nearby San Antonio, the hospital said in a tweet.

Four members of one family were injured. Joann Ward and her three children were hurt, according to a family friend, Gracie Crews, of nearby Stockdale, Texas, who was at the hospital with the family.

Ward was unconscious when officials responded to the scene, and two of the children had to be flown by helicopter to a local hospital, Crews said in a telephone interview. Crews estimated the children were between the ages of 5 and 8, and said that Saturday was Ward and her husband's anniversary.

"We got a call once we heard everything that went down. We rushed to the hospital immediately," Crews said.

Other community members also hurried to help as news of the shooting spread by telephone, social media, "everything," she said. "The community really rushed out."

Eight patients with gunshot wounds were taken to Connally Memorial Medical Center in Floresville, according to spokeswoman Megan Posey.

Four of the eight patients, including one in critical condition, were subsequently transferred to University Hospital, a major trauma center in San Antonio. Three were discharged, and one was listed as stable.

Sutherland Springs is about 35 miles southeast of San Antonio.

"It's a really sad deal, man. I can't describe it," Wilson County Commissioner Albert Gamez Jr. told CBS News, in a phone call from outside the church.

He said the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives were already on the scene assisting investigators. "We've got them all here."

Families gathered outside the church and held hands as they cried and waited for news about the injured and the dead.

House Speaker Paul D. Ryan, R-Wis., called the reports of the shooting "devastating."

"The people of Sutherland Springs need our prayers right now," he said in a tweet.

The small church located in a sparsely populated area of a town of fewer than 700 residents was known for its close sense of community.

It posted its Sunday services regularly on YouTube, and last Sunday's was built around a chapter from the Book of Proverbs and the theme, "You don't need training wheels, you need Christ!"

The service consisted of songs backed by an electric guitar and bass, and a long sermon by Pastor Pomeroy. As the service began, congregants milled about, hugging one another and shaking hands. They were all white, a mix of ages, and it appeared clear they were close. As they greeted one another, the three-person band sang: "God is good, all the time, through the darkest night his light will shine. ... If you're walking through the valley, and there are shadows all around, do not fear, He will guide you, He will keep you safe and sound."

The church is small, and according to the video was dominated last Sunday by Pomeroy's Harley-Davidson motorcycle, parked in front of the pulpit. Pomeroy explained in the video that it was there to illustrate his sermon, which was about "leaning into God" the way a biker leans into a curve, trusting that he won't fall. Pomeroy then described recent rides with his daughter, Annabelle, who is believed to have died in the shooting.

"It's been neat lately ... Annabelle's been wanting to ride with me, and going with me here and there," he said.

He described going out for a ride that morning, when it was 34 degrees out. "She was a trouper; she did not complain. ... She rode, and we had a good time coming in; it was a beautiful ride. Yes, it was a little chilly, but ... the sun was just coming up as we were riding down (County Road) 467 and we saw the sun starting to break over _ that is a beautiful time to be on a motorcycle.... We had a good ride."

Times staff writers Molly Hennessy-Fiske in Cairo, Mitchell Landsberg in Los Angeles and special correspondent Jenny Jarvie in Atlanta contributed to this report.