A man suspected of killing 11 people in a synagogue in the US city of Pittsburgh has been charged with murder.

Robert Bowers, 46, is accused of opening fire at the Tree of Life synagogue during its Sabbath service in what is believed to be the worst antisemitic attack in recent US history.

He faces 29 criminal counts, including use of a firearm to commit murder.

Federal prosecutors said they will also file hate crime charges, and the suspect could face the death penalty.

The shooter entered the Tree of Life Congregation Synagogue in the city's Squirrel Hill neighbourhood at around 10am local time, during a baby-naming service.

Eleven people were killed and many others were injured, including four police officers.

The suspect, who eventually surrendered to police after a shootout, had reportedly shouted "all Jews must die".

Anti-Defamation League President Jonathan Greenblatt said: "This is 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."

President Donald Trump, who said he would visit Pittsburgh soon, described the attack as a "wicked act of mass murder".

He ordered US flags at government buildings to be flown at half-mast until October 31.

He told reporters: “To see this happen again and again, for so many years, it's just a shame.

He said the US should "stiffen up our laws of the death penalty".

"These people should pay the ultimate price. This has to stop.”

US media reported antisemitic social media post from an account with the name Robert Bowers.

A post before the shooting was carried out attacked HIAS, a Jewish agency that resettles refugees.

"HIAS likes to bring in invaders to kill our people," he reportedly wrote.

"I can't sit by and watch our people get slaughtered. Screw your optics. I'm going in."

On Gab, another social media website favoured by the far right, a post read "jews are the children of satan".

FBI special agent Bob Jones told a press conference that Mr Bowers was not know to the authorities prior to the attack.

He said that any motive remains unknown but they believed he was acting alone.