The White House has said it would comment on an explosion that rocked a Minnesota mosque when it has "some kind of finalised investigation".
Sebastian Gorka, deputy assistant to President Donald Trump, said the White House would "wait and see" in case the blast turned out to be a hoax.
The FBI is investigating what Minnesota Governor Mark Dayton has called "a criminal act of terrorism".
Critics pointed out Mr Trump quickly responded after London's terror attack.
Congregants were arriving for prayer early on Saturday when the explosion went off at the Dar Al Farooq Islamic Center in a Minneapolis suburb.
No one was injured in the attack, but the imam's office was heavily damaged and windows were shattered.
FBI officials said the blast was caused by an improvised explosive device.
Mr Trump has yet to issue a statement on the attack, but Mr Gorka defended his boss during an MSNBC interview on Tuesday, saying the administration would wait for a full investigation.
When MSBNC's Stephanie Ruhle pressed Mr Gorka, noting that the president had taken to Twitter in previous attacks before full details were available, he said: "Sometimes an attack is unequivocally clear for what it is.
"When somebody shouts, 'Allahu Akbar', as they're stabbing a police officer, it's pretty clear it's not a case of the mafia robbing a bank, wouldn't you say so?"
He also said "fake hate crimes" have occurred before and the White House should wait for more information.
"Hold your horses, count to 10 and the president will do what he deems fit," Mr Gorka said.
But the president's silence on the attack has drawn criticism from groups including the Council on American-Islamic Relations.
"Silence on the part of public officials at the national level only serves to empower Islamophobes," spokesman Ibrahim Hooper said in a statement to the Los Angeles Times.
"We are wondering why President Trump has not tweeted about this," Asad Zaman, director of the Muslim American Society of Minnesota, told BuzzFeed News.
"He seems to want to tweet about security and terror issues."
The Department of Homeland Security released a statement on Sunday saying that its acting secretary, Elaine Duke, was "aware" of the incident and the agency was in contact with investigators.
"The Department of Homeland Security fully supports the rights of all to freely and safely worship the faith of their choosing and we vigorously condemn such attacks on any religious institution," the statement read.
"We are thankful that there were no injuries, but that does not diminish the serious nature of this act."
Some Twitter users also called on Mr Trump to speak up about the mosque bombing.
Let's say someone yelled Allahu Akbar while throwing an IED bomb into a populated church in Minnesotta. How would President Trump respond?— Wajahat Ali (@WajahatAli) August 7, 2017
Dear @realDonaldTrump,— Michael Skolnik (@MichaelSkolnik) August 6, 2017
There was an act of domestic terrorism at the Dar Al Farooq mosque.
Your silence is deafening.
If a (predominantly white) church or other house of worship were firebombed over the weekend, Trump would've commented by now.— Imraan Siddiqi (@imraansiddiqi) August 7, 2017
An estimated 3.3 million Muslims live in the US, around 1% of the population, according to a recent Pew Research Center report.
Minnesota is home to the largest population of Somalis living in the US and the Dar Al Farooq Islamic Center largely serves people from the Somali community.
Minnesota authorities reported a record high of 14 anti-Muslim bias incidents in 2016, The Star Tribune reported.