US President Donald Trump on Tuesday visited the Tree of Life synagogue in Pittsburgh, where 11 people were gunned down in an anti-Semitic attack during Shabbat services.

Trump was greeted by more than 1,500 protesters who gathered nearby to make it clear the US president was unwelcome.

Carrying signs that read "President Hate, Leave Our State!" and "Trump, Renounce White Nationalism Now," the protesters gathered near synagogue.

Trump, who was accompanied by his wife Melania, arrived in the late afternoon, and placed a white flower and a small stone on each star erected in memory of the dead at a makeshift memorial outside the Tree of Life.

Trump's daughter Ivanka and her husband Jared Kushner, who are Jewish, followed at a short distance, also pausing at each star.

The first couple then entered the synagogue and lit candles in honor of each of those killed, the occasion punctuated by the still audible cries of protesters outside.

The controversial visit came after mourners crowded into nearby synagogues and joined street processions at the first funerals for some of the victims of the deadliest anti-Semitic attack in modern US history.

The service for brothers Cecil and David Rosenthal, both in their 50s, was the first in honor of those killed.

Services for 66-year-old doctor Jerry Rabinowitz and 71-year-old Daniel Stein followed in Pittsburgh, where scores of residents protested Trump's visit.

Suspected shooter Robert Bowers is facing more than two dozen charges related to the bloodshed.

During the 20-minute shooting attack on the synagogue, Bowers fired on congregants and guests with an AR-15 semi-automatic rifle and three handguns. Thirteen people were shot inside the Tree of Life synagogue, 11 of them fatally.

Bowers reportedly made anti-Semitic statements during the shooting, and shouted that “All Jews must die”.

Federal prosecutors said Sunday they would be asking Attorney General Jeff Sessions to give them the green light to pursue a death penalty case against Bowers.

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