The suspect, who was in custody by noon, opened fire inside the Tree of Life Synagogue in the city's Squirrel Hill neighbourhood, according to The Associated Press.
Israeli Prime Minister Benjamin Netanyahu said he was "heartbroken and appalled by the murderous attack on a Pittsburgh synagogue" after a gunman killed at least 11 people and injured six others during religious services on Saturday morning (local time).
"The entire people of Israel grieve with the families of the dead," he said in a video message posted to Twitter after the massacre on Saturday.
"We stand together with the Jewish community of Pittsburgh, we stand together with the American people in the face of this horrendous anti-Semitic brutality, and we all pray for the speedy recovery of the wounded."
Mayor John Fetterman hugs a person as they gather for a vigil in the aftermath of a deadly shooting at the Tree of Life Congregation in Pittsburgh. Photo / AP
Naftali Bennett, Israel's education minister who also oversees diaspora affairs, tweeted that he was on his way to Pittsburgh "to be with our sisters and brothers on their darkest hour."
"When Jews are murdered in Pittsburgh, the people of Israel feel the pain," he wrote.
In a statement, the NZ Jewish Council said it was devastated to learn of the murder of 11 Jews at the Tree of Life Congregation synagogue.
"An attack on Jews anywhere is an attack on Jews everywhere. Our thoughts are with the Jewish community, and all the people of Pittsburgh, and we pray for the recovery of those injured, including police, who acted bravely and swiftly to prevent further bloodshed.
"We will continue to do all we can to fight the scourge of antisemitism, wherever we see it."
As The Washington Post reported on Saturday, Robert Bowers, 46, was taken into custody on Saturday engaging in a gun battle with police at the Tree of Life synagogue in the western Pennsylvania city, where witnesses told police he shouted anti-Semitic slurs and then opened fire with an assault rifle. The attack is being investigated as a hate crime.
People hold candles as they gather for a vigil in the aftermath of the deadly shooting. Photo / AP
The Anti-Defamation League said the shooting was "likely the deadliest attack on the Jewish community in the history of the United States."
The Jerusalem Post quoted Dov Khenin, a member of the Joint List Arab faction in the Knesset, as saying that he suspects "the attack is an expression of the growth of dangerous antisemitism in American society - a part of the racist and violent wave during the presidency of [Donald] Trump. A leadership that gives way to incitement."
Police stand guard outside the Tree of Life Synagogue in Pittsburgh where a shooter opened fire. Photo / AP
Various Israeli leaders offered messages of solidarity with the Pittsburgh Jewish community. Israeli President Reuven Rivlin tweeted that "We are thinking of 'our brothers and sisters, the whole house of Israel, in time of trouble,' as we say in the morning prayers."
President Donald Trump speaks to reporters about a shooting at a Pittsburgh synagogue. Photo / AP
Danny Danon, Israel's ambassador to the United Nations, was quoted in the Jerusalem Post as saying "we will stand together like a rock against hatred and against those who try to harm Jews all over the world."
In Tel Aviv, the municipal building was lit up to resemble the American flag in the aftermath of the shooting.
