Former President Obama called for Americans "to fight the rise of anti-Semitism" after a shooting at a synagogue in Pittsburgh left at least 11 people dead and others wounded.

"We grieve for the Americans murdered in Pittsburgh," Obama said on Twitter Saturday evening. "All of us have to fight the rise of anti-Semitism and hateful rhetoric against those who look, love, or pray differently."

"And we have to stop making it so easy for those who want to harm the innocent to get their hands on a gun," the former president added.

Obama's remarks came hours after authorities say a gunman opened fire at the Pittsburgh-area Tree of Life Synagogue Saturday morning.

Multiple media reports have identified the suspect as 46-year-old Robert Bowers.

Local police say Bowers was taken into custody and transferred later to a hospital after he was wounded in a gunfight with officers.

"It's a very horrific crime scene. It's one of the worst that I've seen," Pittsburgh Public Safety Director Wendell Hissrich said of the attack at a press conference Saturday afternoon.

According to local CBS affiliate KDKA, the suspect made the anti-Semitic remark "all Jews must die" before opening fire at the synagogue.

The Anti-Defamation League said in a statement that the attack was "likely the deadliest attack on the Jewish community in the history of the United States."

"It is simply unconscionable for Jews to be targeted during worship on a Sabbath morning, and unthinkable that it would happen in the United States of America in this day and age," the group wrote.