Senior Border Patrol and Homeland Security officials pushed back again Tuesday at accusations that authorities used excessive force when they lobbed tear gas into Mexico, targeting crowds of migrants, including women and children, who rushed the border fence Sunday.

Video of the fracas show young men throwing rocks toward U.S. border agents before the first wisps of gas appear, though those scenes have been overshadowed by a single photograph of a woman and her barefoot, diapered children fleeing the chaos.

The image has renewed scrutiny of policies espoused by the U.S. Border Patrol, an agency that in recent years has recorded a significant decline in use of lethal force by its agents, statistics show. Incidents involving firearms fell from a high of 55 in 2012 to 17 last year, the result, senior officials say, of improved training, greater restraint and the kinds of tools and tactics deployed Sunday to subdue a frenzied, desperate crowd without causing any significant injuries.

Yet critics of the Trump administration, as well as Mexican officials, have questioned the use of tear gas in the presence of children and the decision to fire canisters over the border fence.

“I can’t imagine firing tear gas into a foreign country,” Gil Kerlikowske, the commissioner of U.S. Customs and Border Protection from 2014 until the end of Barack Obama’s presidency, told The Washington Post. “It’s really a very indiscriminate method, and if you’re firing into Mexico, where there are young families and children, you can’t distinguish if anyone there might have a breathing problem.”

Homeland Security Secretary Kirstjen Nielsen has said the migrants involved in Sunday’s incident were mostly men and that the caravan’s organizers encouraged women and children to go forward, treating them as “human shields.”

Border Patrol agents in 2013 used tear gas to disperse a smaller rock-throwing crowd in Tijuana, but Kerlikowske, who oversaw a broad overhaul of the agency’s use-of-force policies, said he could not recall any such incident during his tenure as commissioner. He said “pepper ball” munitions — which agents also deployed at the border Sunday — were a safer, more precise option because they could be fired directly at bad actors and fence-climbers.

Kerlikowske, a former Seattle police chief, said the use of tear gas in U.S. cities occurs under much different circumstances. “When you use tear gas for crowd control, you have fire [trucks], EMS, ambulances, because it can affect some people more severely than others,” he said.

President Trump, who weeks earlier had suggested that American troops might use lethal force against rock-throwers, has claimed falsely that agents used a less-potent form of gas on the migrants. But Homeland Security officials have since acknowledged that the CS gas they used is the standard-issue variety wielded by police departments and federal agencies in the United States and by authorities around the world.

Last week, the White House issued an order authorizing military personnel to use deadly force in the defense of CBP personnel. On Tuesday, an Army spokesman said that, at the border, only military police who carry firearms as part of their normal duties will be armed and involved in “providing emergency backup,” if asked.

The 1,000 or so people who approached the border fence were a fraction of the more than 5,000 mostly Honduran migrants who have arrived in Tijuana as part of caravans in recent weeks. They have settled there in a squalid campground, with the sinking realization that months could pass before they are allowed to approach the U.S. border crossing to request asylum.

Rodney Scott, the Border Patrol chief for the agency’s San Diego sector, said Tuesday that at the time tear gas was fired, agents had been facing “a direct and immediate threat” from 50 to 100 migrants “throwing rocks and chanting.” Authorities revised the number arrested from 69 to 42.

“The agents responded with the least amount of force that we possibly could,” he said. “We tried the best that we could to target specific instigators we saw throwing rocks or bottles, but I cannot emphasize enough that these were large, moving crowds. . . . This was a very chaotic situation.”

The current CBP commissioner, Kevin McAleenan, said the agency would conduct a standard review of the use of force, but he too has defended the use of tear gas and praised the border agents’ response as effective.

Mexican authorities also called on U.S. officials to investigate the incident, and senior members of the incoming administration of President-elect Andrés Manuel López Obrador, who takes office Saturday, have also objected.

Homeland Security officials say that parents should not have taken their children to a place where out-of-control crowds were trying to force their way into the United States and were attacking U.S. agents. Those families were in the wrong place but were not targeted, said Tyler Houlton, a spokesman for the Department of Homeland Security.

“Border Patrol targeted the violent men who were assaulting officers, destroying federal property and attempting to illegally enter our country,” Houlton told reporters Tuesday. “Others in the area who willingly joined a violent mob committing federal crimes may have been affected by the tear gas unintentionally.”

Kerlikowske, the former CBP commissioner, said he thinks agents should move back from the border fence, away from rock-throwers, whenever possible, rather than engage them.

But Scott said his agents were determined to stand their ground.

U.S. courts have repeatedly upheld agents’ use of force in circumstances where they felt their lives were at risk. Last week in federal court in Arizona, agent Lonnie Swartz was acquitted in the death of a 16-year-old boy he shot through the border fence after coming under attack by rock-throwers. Swartz fired 14 to 30 rounds through the fence, striking the teen 10 times. He argued that he had feared for his life.

Missy Ryan contributed to this report.