While emergency services take care of those who were injured in the attack and police investigate the scene, people have taken to Twitter to share their thoughts on the deadly shooting in the Pittsburgh synagogue.
READ MORE: US Police Detain Pittsburgh Sinagogue Attacker, Confirm Casualties
First Lady Melania Trump also expressed regret at the deadly shooting and called for stopping the violence.
The US president's daughter, Ivanka Trump, called for all Americans to unite against acts of terror and hatred, calling the synagogue shooter a "bigot and anti-Semite."
Israeli Prime Minister, Benjamin Netanyahu extended Israel's condolences to the families affected by the tragedy. He added that Israel stands together with the American people "in the face of horrifying anti-Semitic brutality."
"I am heartbroken and shocked by the murderous attack today at a synagogue in Pittsburgh. The whole of Israel grieves with the families of the dead. We all pray for their rapid recovery," he wrote on his Twitter.
READ MORE: Alleged Pittsburgh Gunman Earlier Touted Anti-Semitic Conspiracies — Reports
Pennsylvania Governor Tom Wolf called the attack an "absolute tragedy" and urged for better gun control in the US.
"We must all pray and hope for no more loss of life. But we have been saying "this one is too many" for far too long. Dangerous weapons are putting our citizens in harm's way," he said.
Most Twitter users either offered prayers for those who were killed and injured in the attack…
…or expressed condolences to relatives of the victims.
Twitter users were shocked by the brutal assault that took place in the synagogue.
Many twitterians were infuriated as they learned that the assailant had shouted "all Jews need to die." They pointed out that anti-Semitism doesn't seem to have been wiped out in society.
A lot of Twitterians instantly called for government action to tackle both mass shootings and anti-Semitism.
An attacker, reportedly carrying an AR-15 rifle and a Glock handgun, entered the Tree of Life Congregation Synagogue in Pittsburgh, Pennsylvania and opened fire on those praying there. According to reports, at least 4 people have been confirmed dead, while estimates as to the total number of casualties vary from 7 to 8.