Self-professed fascist occasionally turned to look and smirked at media present in court during the brief hearing that was held behind closed doors for security reasons.
He did not request bail and was taken into custody until his next court appearance scheduled for April 5.
Israel's Prime Minister Benjamin Netanyahu and President Reuven Rivlin condemned Friday's terror attack on two mosques in Christchurch New Zealand, in which at least 49 worshippers were killed. Police found multiple explosive devices in vehicles stopped as the shootings unfolded; the devices have since been defused.
After Tarrant left the court, the judge said that while "there is one charge of murder brought at the moment, it is reasonable to assume that there will be others".
The Chicago office of the Council on American-Islamic Relations said it was not aware of any threats locally but urged mosques and Muslim centers "to take increased security precautions".
TRT World's Jacob Brown explains.
One man who said he was at the Al Noor mosque told media the gunman burst into the mosque as worshippers were kneeling for prayers.
While the mass shooting was meant to sow fear and division, President Gertler said, "we hope that ultimately those responsible will fail, utterly, in their vicious pursuit". Her foreign minister, Heiko Maas, said: "When people are murdered exclusively due to their religion, this is an attack on us all".
He wrote that he planned to carry out "an attack against the invaders". The country's worst mass shooting was in 1990 when a lone gunman killed 13 people in the small town of Aramoana. He called the attacker an "extremist, right-wing, violent terrorist".
Many cities, including London, Paris and NY, have increased their police presence outside of mosques.
She said questions must also be asked on how the 28-year-old Australian citizen was able to enter New Zealand.
Western leaders from Donald Trump to Angela Merkel expressed solidarity with the people of New Zealand and deplored what the White House called an "act of hate".
The visiting Bangladesh cricket team narrowly avoided the shooting after arriving at the mosque for prayers.
"This individual has travelled around the world with sporadic periods of time spent in New Zealand", Ms Ardern said on Saturday.
Mass shootings, and violent crime in general, are rare in New Zealand, a country of almost 5 million people.
"Horrified to hear of Christchurch mosque shootings". Indian officials have not said whether the nine were believed to be living in Christchurch.
Historical ties with those two countries, as well as a general reaction to those events internationally impacted New Zealand's view on their own national laws.
Christchurch is home to almost 400,000 people and is sometimes called the Garden City.
It said Conservatives stand with Muslims around the world to "reaffirm our commitment to building a world where every people, of every faith, can live in freedom and peace together".
Those "elements" were people affiliated with the Canadian Yellow Vest movement, whose Facebook page included some comments celebrating the New Zealand attacks Friday.