Security at US Conventions was Concern Even Before Nice Attack

— -- The attack in Nice during the city's Bastille Day festivities comes just days before the start of U.S. political conventions that were already raising security concerns.

Hours before the deadly truck attack that killed at least 84 in Nice, law enforcement officials in the U.S. expressed concern about security at the conventions, the first of which, the Republican National Convention, starts Monday in Cleveland.

Authorities have not announced any updates to convention security plans since the Nice attack, but were already preparing for the possibility of violence at demonstrations or other events surrounding the national political gatherings.

"We have to be concerned about things getting out of hand, definitely," Department of Homeland Security Secretary Jeh Johnson said to the House Homeland Security Committee on Thursday morning.

Johnson said the Department of Homeland Security alone is sending about 3,000 people to Cleveland, including personnel from the Secret Service, the Transportation Security Administration, Customs and Border Protection, and the U.S. Coast Guard. A similar contingent will be going to Philadelphia for the Democratic National Convention the following week, according to Johnson.

Johnson himself went to Cleveland today to review preparedness and will do the same in Philadelphia ahead of the Democratic convention.

FBI Director James Comey said, "Anytime there's an event like [a national convention] there is a particular "risk" that comes from domestic terrorists.

The Cleveland police department did not immediately return ABC News' calls about any possible changes to their security plan in light of the attack on Nice.

One thing in Ohio that officials said may present particular challenges is the state's open-carry gun laws. While guns will not be allowed inside the convention center, where the Secret Service will oversee security, the state's laws mandate that people directly outside the building could carry legal weapons.

"That obviously is something that someone under state law and I suspect the 2nd amendment has a right to do," Johnson said. "But it does present a challenging situation very plainly," Johnson said.

ABC News' Mike Levine contributed to this report.