Officials said an 18-year-old gunman opened fire on an elementary school in Texas on Tuesday, killing at least 18 children as he moved from one classroom to another, in the latest horrifying moment for a country that has suffered a series of massacres recently.

But state senator Roland Gutierrez said the death toll in the shooting at the Uvalde school in Texas has risen to 21.

The attacker was killed by law enforcement authorities.

Senator Roland Gutierrez said the death toll also included three adults, and that he received a briefing from state police, but it was not immediately clear whether this number included the attacker or the number of injured.

The massacre that occurred at Robb Elementary School in the predominantly Latino town of Uvalde was the deadliest shooting in an elementary school in the United States since a gunman killed 20 children and six adults at Sandy Hook Elementary School in Newtown, Connecticut, nearly a decade ago.

On the other hand, US President Joe Biden ordered flags to be flown at half-mast in mourning for the victims who died in this incident.