Clinton’s campaign said that “due to the tragic events in Dallas” the Scranton, Pennsylvania, event and a local fundraiser with Biden won’t proceed Friday. The Democratic presidential candidate is expected to address the shootings later in the day at an appearance with the African Methodist Episcopal Convention in Philadelphia.

Clinton tweeted: “I mourn for the officers shot while doing their sacred duty to protect peaceful protesters, for their families & all who serve with them.”

Dallas police said five police officers were killed Thursday night after sniper fire broke out while hundreds of people protested fatal police shootings of two black men this week in Louisiana and Minnesota.

The deaths of the Dallas officers followed the police shootings of Alton Sterling in Baton Rouge, Louisiana, and Philando Castile in suburban St. Paul, Minnesota.

Clinton has made curbing gun violence and ways to improve the criminal justice system a focus of her White House bid, campaigning alongside several women who have lost their children to gun violence or after contact with the police, including the mothers of Trayvon Martin and Eric Garner.

The White House — with Biden deeply involved — has been unable to get Congress to enact stricter gun control measures after several high-profile shootings, including the deaths of 20 children and six staff members at a school in Newtown, Connecticut, in 2012.

Clinton campaigned with President Barack Obama on Tuesday and her planned appearance with Biden in Pennsylvania, a general election battleground state, had been aimed at building party unity before the Democratic National Convention in Philadelphia.