The United States is in mourning after a gunman armed with an assault rifle killed at least 26 people at a church in Texas, among them an 18-month-old baby and elderly worshipper, as debates over the ownership of weapons resurfaced.

Sunday's shooting came little more than one month after the deadliest shooting in recent US history, when a gunman on October 1 killed 58 people attending a concert in Las Vegas.

As vigils for the dead took place, US President Donald Trump, who is visiting Japan, offered condolences and told reporters on Monday: "We have a lot of mental health problems in our country, but this isn't a gun situation."

He described the Texas gunman as "deranged", saying the shooting represented a "mental health problem at the highest level".

The shooting, which took place on Sunday at the First Baptist Church in Sutherland Springs, Texas, was carried out during the 11:00am (17:00 GMT) service.

Officials said that the 26 victims ranged in age from 18 months to 77 years old.

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Freeman Martin, a regional director of the Texas Department of Safety, said that 20 were injured in Sunday's shooting, with 10 people still in critical condition. Martin said those treated in hospitals ranged in age from 5 to 73.

The pastor's 14-year-old daughter and a pregnant woman were also reported to be among the victims.

"It impacts us all. We're a family," said Lee Rios, a resident of Sutherland Springs. "It causes us to stop what we're doing, start to pray, and see how we can serve."

'In-laws attended church'

Sergeant Robert Murphy of the Guadalupe County Sherrif's office confirmed to Al Jazeera that the shooter was deceased.

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Several media outlets have named the suspect as 26-year-old Devin Patrick Kelley, who was dressed in all black at the time of the attack.

He is suspected of killing 23 people inside the church and two outside. One victim died after being transferred to hospital.

Wilson County Sheriff Joe Tackitt Jr. told CNN in an interview on Monday that relatives of Kelley sometimes worshipped at the church but were not there during Sunday's attack.

"We know that his ex-in-laws or in-laws came to church here from time to time," Tackitt Jr. said. "They were not here yesterday."

Authorities said Kelley entered the church and opened fire. He then dropped his weapon and fled the church after a local resident used his own gun to engage. The suspect led police on a brief car chase until he crashed his vehicle.

He was later found dead.

Police said it was unclear whether the suspect took his own life or was killed by officers.

"As a state, we are dealing with the largest mass shooting in our state's history," said Texas Governor Greg Abbott.

Al Jazeera's Heidi Zhou-Castro, reporting from Texas, said fewer than 900 people live in Sutherland Springs.

"The death toll makes up a startling proportion of the population," she said.

'We are not powerless to reduce gun violence'

Politicians, rights groups and social media users said Sunday's shooting was another sign America needed more gun control.

The Mass Shooting Tracker watchdog has recorded at least 24 mass shootings this month and some 1,495 so far this year in the US.

"We'll continue to make history like this until we stop allowing [the National Rifle Association] to control our gun laws," said Gavin Newsom, a Democrat and the lieutenant governor of California, writing on Twitter.

Cory Booker, a US senator from New Jersey, said: "We are not powerless to reduce gun violence in our nation. Congress must act."

Amanda Johnson runs the Texas branch of Moms Demand Action, an organisation that sprouted after the Sandy Hook shooting which aims to end gun violence.

She said: "It cannot be said enough that this is not normal. We should be able to do things like go to worship, go to school or go to a concert without the threat of gun violence. Sadly, no place in our communities is free from that threat."

Johnson explained that Texas has "seen more mass shootings since 2009 than any other state".