Mosques around the United States increased security measures for Friday prayers after a gunman shot dead 49 people and wounded more than 40 at two New Zealand mosques.
Police in New York and other cities said they were stepping up patrols at mosques and other places of worship as a precaution, although there was no sign of any specific threat.
Nihad Awad, head of the Council on American-Islamic Relations (CAIR), said at a Washington news conference that he urged Muslims who would be praying at the more than 3,000 mosques in the United States to "not abandon your mosques."
For years, American Muslims have become used to police patrols, active shooter drills and private security officers guarding mosques for Friday prayers. Security is often ramped up after mass shootings, some of which have taken place at houses of worship, including churches, a synagogue and a gurudwara.
CAIR, the largest Muslim rights group in the United States, said Muslims and other minority groups had faced a surge in bigotry since Donald Trump won the 2016 US presidential election. A CAIR statement blamed this in part on what it described as "Islamophobic, white supremacist and racist Trump administration policies and appointments."
The accused gunman's manifesto posted online praised Trump as "a symbol of renewed white identity and common purpose." The White House did not respond to a request for comment.
"Today, the terrorist has quoted the most powerful person in the world, President Trump," CAIR's Awad said at the news conference. "And I would like to address Mr Trump: Mr Trump, your words matter. Your policies matter. They impact the lives of innocent people at home and globally."
Trump extended condolences for "the horrible massacre" in what the White House called a "vicious act of hate".
Police in New Zealand said three people were in custody, including one man in his late 20s who had been charged with murder for the attack in Christchurch.
Police have not identified any of the suspects. The gunman broadcast his attack live on social media.
CAIR urged worshippers in the United States and abroad to take "stepped-up security precautions."
"There's no such thing as a foolproof plan in a situation like this," Khalid Siddiq, an official at Atlanta's Al-Farooq mosque, said. "We just rely and trust in God."