WASHINGTON — Congressional leaders on Friday voiced dismay and outrage over the killings of police officers in Dallas and called on the American people to unify, and members of the Congressional Black Caucus, while echoing the grief and calls for healing, also demanded that Republicans allow votes to tighten the nation’s gun laws.

“We come to this place each week to represent our constituents who are in pain,” said Representative G.K. Butterfield, Democrat of North Carolina and the chairman of the caucus. “As of June 30, just a few days ago, 491 Americans have been fatally shot by the police; most of those were African-American.”

Mr. Butterfield added, “Last night, despicable crimes were committed against Dallas police officers, and when the dust settled five of them were dead as a result of an organized execution by criminals who possess guns and use them to the extreme. And so the Congressional Black Caucus convenes today to say to America we are continuing our fight to remove guns from the hands of terrorists and would-be criminals.”