YUMA, Ariz. — President Donald Trump deflected any blame from his administration for the deaths of two Guatemalan children this month in U.S. government custody as his Homeland Security chief visited Border Patrol medical officials amid promises of more thorough health screenings for migrant children.

Instead, the president, whose administration has faced widespread criticism over the deaths, pointed the finger on Twitter at Democrats "and their pathetic immigration policies that allow people to make the long trek thinking they can enter our country illegally." They were his first comments on the deaths.

He also tweeted that the children were "very sick before they were given over to Border Patrol."

Any deaths of children or others at the Border are strictly the fault of the Democrats and their pathetic immigration policies that allow people to make the long trek thinking they can enter our country illegally. They can’t. If we had a Wall, they wouldn’t even try! The two..... — Donald J. Trump (@realDonaldTrump) December 29, 2018

...children in question were very sick before they were given over to Border Patrol. The father of the young girl said it was not their fault, he hadn’t given her water in days. Border Patrol needs the Wall and it will all end. They are working so hard & getting so little credit! — Donald J. Trump (@realDonaldTrump) December 29, 2018

The president's comments came Saturday afternoon, the same day Homeland Security Secretary Kirstjen Nielsen was in Yuma, Arizona, to meet with medical staff at the border. Nielsen said in a statement that "the system is clearly overwhelmed and we must work together to address this humanitarian crisis." She called on Congress to "act with urgency."

Her office said she was briefed in El Paso, Texas, on Friday on "recently instituted secondary medical screenings and the more thorough initial health screenings of migrants."

El Paso Mayor Dee Margo said he met with Nielsen and told CNN on Saturday that he agreed with her that the immigration policy is "broken."

"El Paso is dealing with the symptoms as a result of the lack of fortitude in Washington, on both sides of the aisle, to deal with our immigration policy," the Republican said.

Nielsen's trip came days after the death of 8-year-old Felipe Gomez Alonzo in Alamogordo, New Mexico. Felipe was the second Guatemalan child to die in government custody in three weeks. A 7-year-old girl died in El Paso earlier this month.

Nielsen has called the death "deeply concerning and heartbreaking" and requested medical help from other government agencies, including the U.S. Coast Guard. As Nielsen made the trip to Texas, New Mexico's Democratic senators, Tom Udall and Martin Heinrich, sent her a letter Friday seeking answers about the boy's death.

"The timeline, action and factors that led to Felipe's death are still developing, but the information that has become public so far is alarming and demands immediate attention and investigation," the letter says.

Trump blames Dems for migrant kids dying.



No.



DHS told reporters child hasn’t died in CBP custody in 10 years — now two in a month.



Deterrence policy funneling migrants to deadly crossings started under Clinton but *only* targeted families under Trump. pic.twitter.com/vfyEZZi3kt — Jacob Soboroff (@jacobsoboroff) December 29, 2018

U.S. Rep. Raul Grijalva, an Arizona Democrat whose district includes Yuma and much of the U.S.-Mexico-border, on Saturday issued a statement saying Nielsen was visiting Yuma "under the dark cloud of a Republican-induced government shutdown, the president's threats to close the border and the tragic deaths of two children in DHS custody.

Felipe and his father, Agustin Gomez, were apprehended by border agents Dec. 18 near the Paso del Norte bridge connecting El Paso to Juarez, Mexico, according to U.S. Customs and Border Protection. The two were detained at the bridge's processing center and then the Border Patrol station in El Paso, until being taken at about 1 a.m. Sunday to a facility in Alamogordo, New Mexico, about 90 miles away.

Felipe Gomez Alonzo on Dec. 12, 2018 near his half-sister's home in Yalambojoch, Guatemala. Catarina Gomez / via AP

After an agent noticed Felipe coughing, father and son were taken to an Alamogordo hospital, where Felipe was diagnosed with a common cold and found to have a fever of 103 degrees Fahrenheit, CBP has said.

Felipe was held for observation for 90 minutes, according to CBP, before being released with prescriptions for amoxicillin and ibuprofen.

But the boy fell sick hours later on Monday and was re-admitted to the hospital. He died just before midnight.

New Mexico authorities said late Thursday that an autopsy showed Felipe had the flu, but more tests need to be done before a cause of death can be determined.

The government of El Salvador is pushing back against Trump's assertion it doesn't do enough to stem migration north to the United States. The Central American nation says it has made strides in economic and social improvements to try to tamp down the root causes of the phenomenon.

A statement released Saturday said that the Salvadoran government has pushed a media campaign urging its citizens not to risk their lives making the dangerous journey, and especially not to expose children. It says migration from the country has fallen significantly this year.

Trump threatened via Twitter the previous day to cut off aid to El Salvador, Guatemala and Honduras in Central America's so-called Northern Triangle region. He has made similar threats in the past without following through.