CIUDAD JUAREZ, Mexico (Reuters) - Mexico’s National Guard, accused of being heavy-handed in its efforts to curb migrant flows, employed a lighter touch on the U.S. border on Tuesday after President Andres Manuel Lopez Obrador said they did not have orders to detain migrants.

FILE PHOTO: Mexico's President Andres Manuel Lopez Obrador attends a news conference at the National Palace in Mexico City, Mexico June 10, 2019. REUTERS/Gustavo Graf/File Photo

Earlier on Tuesday, Lopez Obrador faced repeated questions at a news conference about photographs that emerged last week of the National Guard catching Central American and Cuban women in Ciudad Juarez, which borders El Paso, Texas.

The photographs showed National Guard members, some armed with rifles, chasing female migrants and detaining them on the Mexican side of the border. Lopez Obrador said they had not been instructed to carry out such detentions.

“There could have been these excesses, but the instruction for everybody is to respect the human rights of migrants, and that will continue,” he said.

By Tuesday afternoon, the message seemed to have reached the National Guard units in Ciudad Juarez.

A Reuters witness said National Guard members in full military gear with automatic rifles watched as a group of 12 adults and four children walked hurriedly under the scorching sun along the dry riverbed of the Rio Grande toward the U.S. border.

A guardsman, who spoke on condition of anonymity, said they were not allowed to arrest the migrants and had instead been directed to read them their rights and advise the people not to go into the United States to seek asylum.

The focus on rights follows other complaints of rough behavior as the new, militarized police force was diverted from fighting cartel crime to containing a wave of mostly Central American migration that prompted U.S. President Donald Trump to threaten tariffs on Mexican goods if the flow is not curbed.

The migrants crossed into the United States at a point along the Ciudad Juarez-El Paso frontier where there is no border wall. After crossing they were immediately detained by U.S. border patrol agents.

Minutes later, a Mexican guardsman approached another group of four migrants who darted towards the border, but abruptly stopped once they crossed over the middle of the dry riverbed, saying Mexico’s jurisdiction ended there - the invisible line separating the two neighboring nations.

Earlier, Lopez Obrador said National Guard members could have committed “excesses” by detaining migrant women close to the U.S. border, and that they had not been instructed to do so.

Mexico has not traditionally used security forces to stop undocumented migrants leaving the country for the United States.

Critics, including political allies of Lopez Obrador, say Mexico is doing too much to placate Trump, after an agreement to stave off the tariff threat that has led to a deployment of more than 20,000 National Guard and soldiers.

Mexico’s army chief said on Monday that 15,000 of those forces are in the north near the U.S. border

The National Guard does have the legal right to detain migrants, Lopez Obrador said, but he explained that it had not been instructed to do so at the northern border.

U.S. Vice President Mike Pence praised Mexico on Tuesday for “keeping its promise” and sending 15,000 troops to border to help with crisis.

“Mexico continues to do more than Congressional Dems to secure our border, and its time for them to STEP UP!,” he said.