'Most evil tweet of 2018': President Donald Trump slammed for blaming Democrats for migrant child deaths

President Donald Trump has come under fire for a tweet in which he claimed Democrats were responsible for the deaths of two migrant children in US custody.

Jakelin Caal, 7, died on December 8 after she and her father were apprehended by border patrol agents. They'd been travelling through the desert with more than 160 other migrants, and Jakelin was suffering from dehydration.

While in custody her father signed documents stating she was healthy, but his lawyers say he didn't understand what he was signing because the forms were in English. Nery Caal also told lawyers that officials didn't give him or his daughter any water for eight hours after they were taken into custody. 

Felipe Gómez Alonzo, 8, died on Christmas Eve after showing flu-like symptoms. His father took him to the border after hearing rumours they would be allowed to migrate to the US and escape their homeland's poverty, the Associated Press reports. He was reportedly in custody for more than 130 hours, which is twice as long as court orders allow. 

The deaths of the two Guatemalan children are under investigation.

Many have blamed the Trump administration's harsh immigration policies for the tragedies, especially with the President's recent fixation with a border wall which has dragged the Government to a shutdown.

Former Secretary of State Hillary Clinton called Jakelin's death a "humanitarian crisis", while Congressman Beto O'Rourke said current immigration policies are causing "suffering and death".

President Trump has lashed out at the criticism, and in a tweet on Saturday (local time) blamed Democrats for the children's deaths.

"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," he wrote.

"They can't. If we had a Wall, they wouldn't even try!"

In a follow-up tweet he also blamed Jakelin's father for not giving her water as they walked to the border. It's the first time he has publicly acknowledged the deaths.

His comments have been met with disgust on social media, with several high-profile celebrities condemning the President.

Actor Patton Oswalt called the statement the "most evil tweet of 2018".

"More lies," said actress Mia Farrow. "But we expect only lies from Trump."

New Zealand's own Taika Waititi also weighed in with a quote from his film Thor: Ragnarok: "Piss off, ghost."

Some Twitter users replied to the President's tweet calling him "soulless" and "cruel", while others urged him to take responsibility for how his own party implements border policies.

US federal law allows anyone who reaches US soil, regardless of their immigration status, to apply for asylum if they fear persecution in their home country.