"This is not a time to lash out, to incite fear, or to use tragedy and terror for political gain," Clinton said at a fundraiser for an organization that builds ties between African-American and Jewish youths.
In a clear reference to Trump's tweets Sunday and Monday criticizing London Mayor Sadiq Khan, Clinton said: "It's a time for steady, determined leadership -- like we are seeing from local authorities in London, including the mayor of London."
Trump has repeatedly twisted Khan's words on Twitter.
Khan had told London's citizens that there was no cause for alarm about increased police presence in the city in the coming days following an attack on the London Bridge that killed at least seven people.
But Trump seized on only a small portion of Khan's remarks, tweeting Sunday: "At least 7 dead and 48 wounded in terror attack and Mayor of London says there is 'no reason to be alarmed!'"
Then, on Monday, he combined another shot at Khan with criticism of the mainstream media, tweeting: "Pathetic excuse by London Mayor Sadiq Khan who had to think fast on his "no reason to be alarmed" statement. MSM is working hard to sell it!"
Trump's former Democratic presidential opponent has emerged as a top critic of the President's actions since he took office -- increasingly using her speeches and public appearances to push back on policies coming out of the White House.
On Monday, Clinton called for strengthened ties with global allies -- a clear contrast with Trump, who has in recent days alarmed NATO allies and withdrawn the United States from a Paris climate accord.
"It's even more important that we work together with our allies and our friends and our partners -- yes, to keep us safe, but also to expand our understanding of what we can achieve together," Clinton said.
Her comments came at a fundraiser for the Elijah Cummings Youth Program in Israel -- a fellowship aimed at building ties between the black and Jewish communities headed by Cummings, a Maryland Democratic congressman, and the Baltimore Jewish Council. It was held at the Frederick Douglass-Isaac Myers Maritime Park.
Clinton also addressed recent racially motivated attacks in Oregon and Maryland.
"At a time when anti-Semitic hate crimes are on the rise -- when Americans, Muslims, African-Americans, Latinos are being targeted for racism; when violence motivated by hatred from Portland, Oregon, to College Park, ends the lives of young Americans, this program's vision of spreading tolerance is more urgent than ever," Clinton said.