The president suggested the person responsible should face the death penalty.
“I think one thing we should do is we would stiffen up our laws with guns with the death penalty,” Trump said.
“When people do this they should get the death penalty.”
He said those responsible for such crimes should “pay the ultimate price” without having to wait “years and years.”
At least 11 people are dead and more injured, including police officers. One man has been taken into custody; authorities say they believe he is the lone suspect.
“It’s a terrible, terrible thing that’s been going on with hate in our country and frankly all over the world, and something has to be done,” Trump said.
WATCH: ‘We could hear the shots,’ say residents near scene of Tree of Life synagogue shooting
While there is no indication the two incidents are connected, the synagogue shooting comes after a tense week in which a number of prominent Democrats and CNN were sent pipe bombs; a man arrested Friday in the case is a staunch Trump supporter.
At first, Trump called for unity before blaming “the mainstream media” for anger in America and suggesting the bombs were an attempt to distract from the upcoming midterm elections.
While details regarding Saturday’s tragic event continues to emerge, Trump praised police response and referred to the accused gunman as a “madman” and “whacko.”
Tree of Life Congregation Synagogue is located in Pittsburgh’s Squirrel Hill neighbourhood. Jeff Finkelstein, CEO of Jewish Federation of Greater Pittsburgh, told reporters that on a typical Saturday morning about 50 or 60 people worship at the synagogue.
The state’s attorney general said the “shooter claimed innocent lives” at a baby naming ceremony.
The FBI has taken over the investigation and the shooting is being considered a hate crime, according to officials.
Pittsburgh public safety director Wendell Hissrich appeared shaken when describing to reporters what he’d seen inside the synagogue.
“It’s a very horrific crime scene, one of the worst that I’ve seen,” said Hissrich.
WATCH: Multiple people dead, suspect in custody after Pittsburgh synagogue shooting
Robert Bowers, 46, has been arrested. Multiple reports say Bowers allegedly made anti-Semitic remarks during and after the crime.
On Saturday afternoon, Trump said the “vile hateful poison” of anti-Semitism must be condemned.
The victims’ identities have not been released, though officials say no children were killed.
— This is a developing story and will be updated as more information becomes available. With files from Reuters and Global News reporter Rahul Kalvapalle.