In one tweet, Trump appeared to criticize London Mayor Sadiq Khan for attempting to reassure his city's residents in the aftermath of the attack Saturday night that killed seven and injured dozens. The mayor said, "Londoners will see an increased police presence today and over the course of the next few days. No reason to be alarmed."
Trump responded with a tweet, "At least 7 dead and 48 wounded in terror attack and Mayor of London says there is "no reason to be alarmed!"
A spokesperson for Khan, the city's first Muslim mayor, called Trump's remark "ill-informed" on Sunday and said it took the mayor's words out of context.
"The Mayor is busy working with the police, emergency services, and the government to coordinate the response to this horrific and cowardly terrorist attack and provide leadership and reassurance to Londoners and visitors to our city," the spokesperson said in a statement.
"He has more important things to do than respond to Donald Trump's ill-informed tweet that deliberately takes out of context his remarks urging Londoners not to be alarmed when they saw more police - including armed officers - on the streets."
Another of Trump's tweets suggested that in light of such terrorist attacks, the U.S. needs to implement his executive order temporarily restricting entry into the U.S. by people from six predominantly Muslim countries.
The executive order, now in its second version, has been blocked by the U.S. Court of Appeals for the 4th Circuit, which declined to lift a lower court's stay of the order.
The ACLU, which sued to block the executive order, replied to Trump by quoting his tweet and added, "Glad we both agree the ban is a ban," an apparent reference to an argument by the travel order's opponents that its true intent is to ban the entry of Muslims into the U.S.
Omar Jadwat, director of the ACLU's Immigrants' Rights Project and who argued the 4th Circuit case opposing the executive order, told ABC News that there isn't a comparable court case to the one against the travel order in part because of what Trump says on Twitter and in speeches.
"Ordinarily, it's hard to prove that things are done with an improper purpose because the decision makers cover their tracks with very careful wording," Jadwat said. "What Trump says about his own intentions is unusual."