Donald Trump has claimed that immigrants crossing the border illegally will “infest” America without strong laws, as the outcry over a policy of separating families at the border continues to build.

The family separations are part of a “zero tolerance” policy of dealing with illegal border crossings, where all adults are prosecuted – leaving any children to be housed in detention centres while cases are processed. The policy was announced last month by Attorney General Jeff Sessions but is not codified in US immigration law, particularly that relating to seeking asylum.

Images of children fenced in, in wire mesh cages, and audio of screaming young boys and girls being separated from their parents has led to a backlash from Democrats and some within Mr Trump’s own Republican party.

Democrats have hurled charges of “barbaric” treatment of children and decrying what they have labelled harsh and demeaning language the president as used, with Mr Trump falsely blaming them for not helping Congress deal with the issue of the separations.

He returned to that accusation in his morning tweet: “Democrats are the problem. They don’t care about crime and want illegal immigrants, no matter how bad they may be, to pour into and infest our Country, like MS-13. They can’t win on their terrible policies, so they view them as potential voters!”

Mr Trump has constantly sought to contrast what he claims are soft Democrat positions with his hardline, and controversial, stance on immigration, often using hyperbole. The reference to the MS-13 gang is a callback to his election promise to rid the country of members of the violent group, which has its origins in Central America. That promise was a central pillar of his 2016 election campaign.

Later, during remarks to the National Federation of Independent Businesses, Mr trump again sought to blame Democrats for what he called “loopholes“ in the law that require families detained for entering the country illegally either to be separated or released.

“These are crippling loopholes that cause family separation, which we don’t want,” he said, adding he wanted Congress to give him the legal authority to detain and deport families together.

Given the president’s promises on immigration, Trump administration officials – such as Mr Sessions and Department of Homeland Security Secretary Kirstjen Nielsen – have said they “will not apologise” for following the law and it is up to Congress to being new legislation to change the rules.

More than 2,300 children were separated from their parents from 5 May to 9 June, according to Department of Homeland Security figures. With potentially hundreds more separated thanks to a policy that started in mid-April.

CNN political analyst Brian Karem presses White House press secretary Sarah Sanders on family separations at the US-Mexico border

Mr Trump travelled to Congress on Tuesday evening to discuss wider immigration reform with Republicans. Ahead of that visit two top conservatives announced they would be introducing bills to stop the practice of the separations.

Senator Ted Cruz of border state Texas introduced legislation that the White House said it was reviewing, and Representative Mark Meadows of North Carolina, a leader of the conservative Freedom Caucus, also introduced a measure.

Both bills were offered as alternatives in case broader GOP immigration legislation heading for a vote this week fails, as is likely. “This becomes a backup proposal,” Mr Meadows told reporters at the White House.

Two Republican bills are currently having the finishing touches to them by Mr Trump’s party. The first is a hard-right proposal, the second the more moderate plan negotiated by the party’s conservative and centrist wings, with White House input.

Only the latter would open a door to citizenship for young immigrants brought to the US illegally as children, and reduce the separation of children from their parents when families are detained crossing the border. Leaders released a schedule for next week that included “possible consideration” of immigration legislation.

President Trump sought to link an end to the family separations to passage of a wider bill on immigration during his appearances on Tuesday, prompting Democrats to accuse him of using children as hostages.

Undocumented immigration across the US-Mexico border Show all 14 1 /14 Undocumented immigration across the US-Mexico border Undocumented immigration across the US-Mexico border Immigrant children, many of whom are separated form their parents, are housed in Texas' tent city Reuters Undocumented immigration across the US-Mexico border A two-year-old Honduran asylum seeker cries as her mother is searched and detained near the US-Mexico border Getty Undocumented immigration across the US-Mexico border Undocumented migrants ride on the top of a freight train referred to as the beast, or La Bestia Getty Undocumented immigration across the US-Mexico border A cage inside a US Customs and Border Protection detention facility in Texas Reuters Undocumented immigration across the US-Mexico border US Border Patrol Academy All new agents must complete a months-long training course at the New Mexico facility before assuming their posts at Border Patrol stations, mostly along the US-Mexico border Getty Undocumented immigration across the US-Mexico border US-Mexico border fence A group of young men walk along the Mexican side of the US-Mexico border fence in a remote area of the Sonoran Desert Getty Undocumented immigration across the US-Mexico border US-Mexico border fence in the US Man looks through US-Mexico border fence into the US in Tijuana, Mexico Getty Undocumented immigration across the US-Mexico border US-Mexico border fence US Border Patrol agent Sal De Leon stands near a section of the US-Mexico border fence while stopping on patrol on in La Joya, Texas Getty Undocumented immigration across the US-Mexico border US Border Patrol Academy US Border Patrol instructor yells at trainees after their initial arrival to the academy Getty Undocumented immigration across the US-Mexico border Memorial service in Guatemala Families attend a memorial service for two boys who were kidnapped and killed in San Juan Sacatepequez, Guatemala. Crime drives emigration from Guatemala to the United States, as families seek refuge from the danger Getty Undocumented immigration across the US-Mexico border Arrests on the border Undocumented immigrants comfort each other after being caught by Border Patrol agents near the US-Mexico border Getty Undocumented immigration across the US-Mexico border Detention holding facility A boy from Honduras watches a movie at a detention facility run by the US Border Patrol Getty Undocumented immigration across the US-Mexico border Mexican farm workers Mexican migrant workers harvest organic parsley at Grant Family Farms in Wellington, Colorado Getty Undocumented immigration across the US-Mexico border Mexican family in Arizona A Mexican immigrant family sits in the living room of their rented home in Tuscon, Arizona. The family that Arizona's new tough immigrant law had created a climate of fear in the immigrant community. Getty

Tensions high in Congress, with the border issuing affecting a House hearing on an unrelated subject when protesters with babies briefly shut down proceedings.

Maryland Representative Elijah Cummings, the top Democrat on the House Oversight and Government Reform Committee, teared up as he pleaded with Republicans on the panel to end what he called “internment camps” for those crossing the border.

“We need you, those children need you —and I am talking directly to my Republican colleagues— we need you to stand up to President Donald Trump,” he said.

Criticism of the policy has come from all sides. All five living US first ladies including Laura Bush, wife of Republican President George W Bush, and Melania Trump have made clear feelings over the policy. Ms Bush, who has been the first lady of the state of Texas as well, called the policy “cruel” while Ms Trump said she “hates to see” children separated from their parents.

Internationally, France’s government spokesman called the images of the children in detention centres “shocking” and that the policy shows the US and Europe now has different “values” on certain issues..

“We do not share the same model of civilisation, clearly we don’t share certain values,” Benjamin Griveaux told France 2 television.

Mexico’s foreign minister Luis Videgaray called the separations “cruel and inhumane” and urged the United States to reconsider the practice. “This is a clear violation of human rights and puts children, including those with disabilities, in a vulnerable situation,” Mr Videgaray told a news conference in Mexico City. Mr Trump claimed on Tuesday that Mexico “do nothing” to help the situation on the border.

Among the 21 identified cases of Mexicans separated from their parents was a 10-year-old girl with Down Syndrome who was being held in McAllen, Texas, MrVidegaray said, with her mother being taken to another place.

Most of the children are from Central America, especially Guatemala, Honduras and El Salvador. Honduras has called for Washington to end the separations, and El Salvador said the policy puts children’s health at risk and could cause psychological scars.

Despite Mr Trump and his surrogates’ claims, the administration actually has unilateral ability to rescind the policy. The president’s claim that “it’s Democrats’ law” is false. There is no clause in current US immigration law or court precedent that compels family separation. The Obama and Bush administrations had been housing children, as Trump officials have claimed, but those were unaccompanied minors who had fled the violence of their home countries and crossed the border without any adults.

The previous administrations were also arresting people travelling in families, but it was not immediate and parents had the chance to formally apply for asylum – for which you have to be in the US to do per the law – and could remain in the country while waiting for their hearing. This is what was referred to as the “catch and release” policy Mr Trump has vilified.

The Democrat leader in the Senate, Chuck Schumer said legislation to end the separations was “not the way to go” as the Trump administration could change the policy on its own.

White House press secretary Sarah Huckabee Sanders justified the policy late last week by describing it as biblical: “It is very biblical to enforce the [particular immigration] law, that is actually repeated a number of times throughout the Bible.” Several church groups have criticised the policy as needlessly harmful to children.

But the issue will likely dominate the airwaves and other media until a solution is found. The attorneys general of 21 states called on Jeff Sessions in a letter released on Tuesday to stop endangering children by separating them from their families.