TIJUANA (Reuters) - After nearly two weeks of documenting the harrowing journey of a caravan of mostly Central American migrants headed toward the U.S.-Mexican border, I snapped a picture I will never forget.

In the shot, taken on Sunday, you can see Honduran mother Maria Meza grabbing the thin arms of her two 5-year-old twin daughters Cheili and Saira as they frantically run from a tear gas canister spewing fumes.

Cheili is seen in diapers, Saira barefoot, while their mother wears a T-shirt showing the smiling sisters from the Disney hit “Frozen,” a movie I’ve seen many times with my own daughter.

Meza’s daughter, Jamie, is behind her mother in the photo, also running away from the approaching gas. According to their Honduran documents, Meza is 40 and her daughter is 12.

In the frantic moments after the canisters hit the ground, the acrid smell was everywhere and I could see children crying, their eyes stung by the gas.

“I thought I was going to die with them because of the gas,” Meza told my Reuters colleagues a day later, adding that she was shocked U.S. border agents would fire the canisters near women and children.

The U.S. government said the customs officers had fired off the canisters after a group of migrants had attempted to cross the border violently, throwing projectiles at them.

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I did not see who fired the canister but I heard the sound come from the direction of the fence and I began running too. It was one of the first of several tear gas canisters I saw used. At that point, I had not seen any of the migrants throw projectiles but it is a large area and things were happening in different places.

I cannot say which side is right, and which is wrong. I just took a photo of what I saw at that moment and in that location.

Some social media users have called the photo "staged," which absolutely is not the case. At Reuters, we have strict photo guidelines. We are not allowed here to mislead the viewer by making material alterations or staging scenes.

Reuters has core values here of independence, freedom from bias, and accuracy. I am proud to uphold those sacrosanct values.

Meza’s family had made it to the El Chaparral border crossing, which straddles the Mexican city of Tijuana and San Diego on the U.S. side, after leaving their home in the violent city of San Pedro Sula in northern Honduras two months ago.

Sunday’s incident happened after a group of migrants in Tijuana rushed at the border fencing.

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Just before the tear gas was fired, I had followed some of the migrants as they approached a section of the border fence recently reinforced with razor-studded coils. U.S. border agents warily eyed the group from the other side.

Meza and her children said they had already spent a week at a Tijuana shelter, but they will likely have to wait much longer for a chance to ultimately plead their case.

She said she hopes to be granted asylum in the United States due to rampant crime back home, and if successful will travel to Louisiana, where the girls’ father lives.

Photo essay: reut.rs/2Q0pnVp