President Mahmoud Abbas wrote to US President Barack Obama on Saturday to offer his condolences after a shooting in an American elementary school killed 26 people.

Twenty children were killed by a heavily armed gunman who opened fire at a school in Newtown, Connecticut, on Friday. He killed at least 26 people there before turning his gun on himself.

Authorities found 18 children and seven adults, including the gunman, dead at the school, and two children were pronounced dead later after being taken to a hospital.

"Most of those who died were just young children with their whole lives ahead of them. And every parent in America has a heart heavy with hurt," Obama said.

Abbas expressed his condolences for the American people and the families of the victims, Palestinian Authority news agency Wafa said.